diff --git a/src/main/java/io/github/depromeet/knockknockbackend/domain/group/domain/repository/GroupUserRepository.java b/src/main/java/io/github/depromeet/knockknockbackend/domain/group/domain/repository/GroupUserRepository.java
index dc4d7ccc..7872054d 100644
--- a/src/main/java/io/github/depromeet/knockknockbackend/domain/group/domain/repository/GroupUserRepository.java
+++ b/src/main/java/io/github/depromeet/knockknockbackend/domain/group/domain/repository/GroupUserRepository.java
@@ -1,8 +1,14 @@
 package io.github.depromeet.knockknockbackend.domain.group.domain.repository;
 
 
+import io.github.depromeet.knockknockbackend.domain.group.domain.Group;
 import io.github.depromeet.knockknockbackend.domain.group.domain.GroupUser;
+import io.github.depromeet.knockknockbackend.domain.user.domain.User;
+import java.util.Optional;
 import org.springframework.data.jpa.repository.JpaRepository;
 
 public interface GroupUserRepository
-        extends JpaRepository<GroupUser, Long>, CustomGroupUserRepository {}
+        extends JpaRepository<GroupUser, Long>, CustomGroupUserRepository {
+
+    Optional<GroupUser> findByGroupAndUser(Group group, User user);
+}
diff --git a/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/domain/Reservation.java b/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/domain/Reservation.java
index 18b0ac63..5fc82470 100644
--- a/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/domain/Reservation.java
+++ b/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/domain/Reservation.java
@@ -14,7 +14,9 @@
 @AllArgsConstructor(access = AccessLevel.PRIVATE)
 @NoArgsConstructor(access = AccessLevel.PROTECTED)
 @DynamicUpdate
-@Table(name = "tbl_reservation")
+@Table(
+        name = "tbl_reservation",
+        uniqueConstraints = {@UniqueConstraint(columnNames = {"group_id", "send_user_id"})})
 @Entity
 public class Reservation extends BaseTimeEntity {
 
diff --git a/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/domain/repository/ReservationRepository.java b/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/domain/repository/ReservationRepository.java
index 0373eac1..32853b7f 100644
--- a/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/domain/repository/ReservationRepository.java
+++ b/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/domain/repository/ReservationRepository.java
@@ -6,13 +6,14 @@
 import io.github.depromeet.knockknockbackend.domain.user.domain.User;
 import java.time.LocalDateTime;
 import java.util.List;
+import java.util.Optional;
 import org.springframework.data.jpa.repository.Modifying;
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.repository.CrudRepository;
 import org.springframework.data.repository.query.Param;
 
 public interface ReservationRepository extends CrudRepository<Reservation, Long> {
-    List<Reservation> findByGroupAndSendUserOrderBySendAtAsc(Group group, User sendUser);
+    Optional<Reservation> findByGroupAndSendUser(Group group, User sendUser);
 
     List<Reservation> findBySendAtLessThan(LocalDateTime sendAt);
 
diff --git a/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/exception/ReservationAlreadyExistException.java b/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/exception/ReservationAlreadyExistException.java
new file mode 100644
index 00000000..8d79d513
--- /dev/null
+++ b/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/exception/ReservationAlreadyExistException.java
@@ -0,0 +1,13 @@
+package io.github.depromeet.knockknockbackend.domain.notification.exception;
+
+
+import io.github.depromeet.knockknockbackend.global.error.exception.ErrorCode;
+import io.github.depromeet.knockknockbackend.global.error.exception.KnockException;
+
+public class ReservationAlreadyExistException extends KnockException {
+    public static final KnockException EXCEPTION = new ReservationAlreadyExistException();
+
+    private ReservationAlreadyExistException() {
+        super(ErrorCode.RESERVATION_ALREADY_EXIST);
+    }
+}
diff --git a/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/presentation/dto/response/QueryNotificationListResponse.java b/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/presentation/dto/response/QueryNotificationListResponse.java
index cacd8572..3c78a408 100644
--- a/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/presentation/dto/response/QueryNotificationListResponse.java
+++ b/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/presentation/dto/response/QueryNotificationListResponse.java
@@ -1,7 +1,6 @@
 package io.github.depromeet.knockknockbackend.domain.notification.presentation.dto.response;
 
 
-import java.util.List;
 import lombok.AllArgsConstructor;
 import lombok.Getter;
 import org.springframework.data.domain.Slice;
@@ -10,6 +9,6 @@
 @AllArgsConstructor
 public class QueryNotificationListResponse {
 
-    private final List<QueryReservationListResponseElement> reservations;
+    private final QueryReservationListResponseElement reservations;
     private final Slice<QueryNotificationListResponseElement> notifications;
 }
diff --git a/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/service/NotificationService.java b/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/service/NotificationService.java
index d5558924..2f173639 100644
--- a/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/service/NotificationService.java
+++ b/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/service/NotificationService.java
@@ -2,7 +2,11 @@
 
 
 import io.github.depromeet.knockknockbackend.domain.group.domain.Group;
+import io.github.depromeet.knockknockbackend.domain.group.domain.GroupType;
+import io.github.depromeet.knockknockbackend.domain.group.domain.repository.GroupUserRepository;
+import io.github.depromeet.knockknockbackend.domain.group.exception.NotMemberException;
 import io.github.depromeet.knockknockbackend.domain.group.presentation.dto.response.GroupInfoForNotificationDto;
+import io.github.depromeet.knockknockbackend.domain.group.service.GroupService;
 import io.github.depromeet.knockknockbackend.domain.notification.domain.*;
 import io.github.depromeet.knockknockbackend.domain.notification.domain.Notification;
 import io.github.depromeet.knockknockbackend.domain.notification.domain.repository.DeviceTokenRepository;
@@ -38,11 +42,13 @@ public class NotificationService implements NotificationUtils {
     private static final boolean CREATED_DELETED_STATUS = false;
     private final EntityManager entityManager;
     private final FcmService fcmService;
+    private final GroupService groupService;
     private final NotificationRepository notificationRepository;
     private final DeviceTokenRepository deviceTokenRepository;
     private final NotificationReactionRepository notificationReactionRepository;
     private final ReservationRepository reservationRepository;
     private final NotificationExperienceRepository notificationExperienceRepository;
+    private final GroupUserRepository groupUserRepository;
 
     @Transactional(readOnly = true)
     public QueryNotificationListLatestResponse queryListLatest() {
@@ -79,11 +85,10 @@ public QueryNotificationListResponse queryListByGroupId(Pageable pageable, Long
                                 getQueryNotificationListResponseElements(
                                         notification, myNotificationReactions));
 
-        List<Reservation> reservations =
-                reservationRepository.findByGroupAndSendUserOrderBySendAtAsc(
-                        Group.of(groupId), User.of(SecurityUtils.getCurrentUserId()));
-        List<QueryReservationListResponseElement> queryReservationListResponseElements =
-                reservations.stream()
+        QueryReservationListResponseElement queryReservationListResponseElement =
+                reservationRepository
+                        .findByGroupAndSendUser(
+                                Group.of(groupId), User.of(SecurityUtils.getCurrentUserId()))
                         .map(
                                 reservation ->
                                         QueryReservationListResponseElement.builder()
@@ -93,10 +98,10 @@ public QueryNotificationListResponse queryListByGroupId(Pageable pageable, Long
                                                 .imageUrl(reservation.getImageUrl())
                                                 .sendAt(reservation.getSendAt())
                                                 .build())
-                        .collect(Collectors.toList());
+                        .orElse(null);
 
         return new QueryNotificationListResponse(
-                queryReservationListResponseElements, queryNotificationListResponseElements);
+                queryReservationListResponseElement, queryNotificationListResponseElements);
     }
 
     public QueryNotificationListResponseElement getQueryNotificationListResponseElements(
@@ -168,9 +173,10 @@ public void registerFcmToken(RegisterFcmTokenRequest request) {
 
     @Transactional
     public void sendInstance(SendInstanceRequest request) {
-        Long sendUserId = SecurityUtils.getCurrentUserId();
+        Long currentUserId = SecurityUtils.getCurrentUserId();
+        validateSendNotificationPermission(request.getGroupId(), currentUserId);
 
-        List<DeviceToken> deviceTokens = getDeviceTokens(request.getGroupId(), sendUserId);
+        List<DeviceToken> deviceTokens = getDeviceTokens(request.getGroupId(), currentUserId);
         List<String> tokens = getFcmTokens(deviceTokens);
         if (tokens.isEmpty()) {
             return;
@@ -185,7 +191,7 @@ public void sendInstance(SendInstanceRequest request) {
                 request.getContent(),
                 request.getImageUrl(),
                 Group.of(request.getGroupId()),
-                User.of(sendUserId),
+                User.of(currentUserId),
                 null);
     }
 
@@ -241,6 +247,19 @@ private void validateDeletePermission(Notification notification) {
         }
     }
 
+    public void validateSendNotificationPermission(Long groupId, Long userId) {
+        Group group = groupService.queryGroup(groupId);
+        // 홀로외침방이면 방장인지
+        if (GroupType.OPEN.equals(group.getGroupType())) group.validUserIsHost(userId);
+        // 친구방이면 그룹 소속원인지
+        if (GroupType.FRIEND.equals(group.getGroupType())) {
+            // group.validUserIsMemberOfGroup(userId); //todo: 해당 부분 호춣시 불필요한 쿼리 발생.
+            groupUserRepository
+                    .findByGroupAndUser(group, User.of(userId))
+                    .orElseThrow(() -> NotMemberException.EXCEPTION);
+        }
+    }
+
     @Override
     public Notification queryNotificationById(Long notificationId) {
         return notificationRepository
diff --git a/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/service/ReservationService.java b/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/service/ReservationService.java
index 4825fe0d..d1d16c2c 100644
--- a/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/service/ReservationService.java
+++ b/src/main/java/io/github/depromeet/knockknockbackend/domain/notification/service/ReservationService.java
@@ -5,6 +5,7 @@
 import io.github.depromeet.knockknockbackend.domain.notification.domain.DeviceToken;
 import io.github.depromeet.knockknockbackend.domain.notification.domain.Reservation;
 import io.github.depromeet.knockknockbackend.domain.notification.domain.repository.ReservationRepository;
+import io.github.depromeet.knockknockbackend.domain.notification.exception.ReservationAlreadyExistException;
 import io.github.depromeet.knockknockbackend.domain.notification.exception.ReservationForbiddenException;
 import io.github.depromeet.knockknockbackend.domain.notification.exception.ReservationNotFoundException;
 import io.github.depromeet.knockknockbackend.domain.notification.presentation.dto.request.ChangeSendAtReservationRequest;
@@ -32,6 +33,16 @@ public class ReservationService {
 
     public void sendReservation(SendReservationRequest request) {
         Long currentUserId = SecurityUtils.getCurrentUserId();
+        notificationService.validateSendNotificationPermission(request.getGroupId(), currentUserId);
+        Reservation reservation =
+                reservationRepository
+                        .findByGroupAndSendUser(
+                                Group.of(request.getGroupId()), User.of(currentUserId))
+                        .orElse(null);
+
+        if (reservation != null) {
+            throw ReservationAlreadyExistException.EXCEPTION;
+        }
 
         reservationRepository.save(
                 Reservation.of(
diff --git a/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/domain/repository/CustomRelationRepository.java b/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/domain/repository/CustomRelationRepository.java
index 3accd30f..b194bc4f 100644
--- a/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/domain/repository/CustomRelationRepository.java
+++ b/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/domain/repository/CustomRelationRepository.java
@@ -12,4 +12,6 @@ Optional<Relation> findRelationBySendUserIdAndReceiveUserId(
             Long sendUserId, Long receiveUserId);
 
     boolean isFriend(Long currentUserId, Long userId);
+
+    Long getRelationIdByUserId(Long currentUserId, Long userId);
 }
diff --git a/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/domain/repository/CustomRelationRepositoryImpl.java b/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/domain/repository/CustomRelationRepositoryImpl.java
index 353a9a8b..f8457837 100644
--- a/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/domain/repository/CustomRelationRepositoryImpl.java
+++ b/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/domain/repository/CustomRelationRepositoryImpl.java
@@ -55,6 +55,17 @@ public boolean isFriend(Long currentUserId, Long userId) {
                 .fetchFirst();
     }
 
+    @Override
+    public Long getRelationIdByUserId(Long currentUserId, Long userId) {
+        return queryFactory
+                .select(relation.id)
+                .from(relation)
+                .where(
+                        friendPredicated(currentUserId, userId)
+                                .or(friendPredicated(userId, currentUserId)))
+                .fetchFirst();
+    }
+
     private BooleanExpression friendPredicated(Long senderUserId, Long receiveUserId) {
         return relation.sendUser.id.eq(senderUserId).and(relation.receiveUser.id.eq(receiveUserId));
     }
diff --git a/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/exception/NotFriendRelationException.java b/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/exception/NotFriendRelationException.java
new file mode 100644
index 00000000..cc446cc9
--- /dev/null
+++ b/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/exception/NotFriendRelationException.java
@@ -0,0 +1,14 @@
+package io.github.depromeet.knockknockbackend.domain.relation.exception;
+
+
+import io.github.depromeet.knockknockbackend.global.error.exception.ErrorCode;
+import io.github.depromeet.knockknockbackend.global.error.exception.KnockException;
+
+public class NotFriendRelationException extends KnockException {
+
+    public static final KnockException EXCEPTION = new NotFriendRelationException();
+
+    private NotFriendRelationException() {
+        super(ErrorCode.NOT_FRIEND_RELATION);
+    }
+}
diff --git a/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/presentation/RelationController.java b/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/presentation/RelationController.java
index 92508b55..ac770d9f 100644
--- a/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/presentation/RelationController.java
+++ b/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/presentation/RelationController.java
@@ -40,6 +40,13 @@ public ResponseEntity<Void> sendUserRequest(@RequestBody @Valid FriendRequest re
         return new ResponseEntity<>(relationService.sendFriendRequest(request));
     }
 
+    @Operation(summary = "친구를 삭제하는 Api입니다. - 친구목록")
+    @ResponseStatus(HttpStatus.NO_CONTENT)
+    @DeleteMapping
+    public void deleteRelation(@RequestBody @Valid FriendRequest request) {
+        relationService.deleteRelation(request);
+    }
+
     @Operation(summary = "친구 요청을 수락하는 Api입니다. - 메인 알림")
     @ResponseStatus(HttpStatus.CREATED)
     @PostMapping("/requests")
diff --git a/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/service/RelationService.java b/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/service/RelationService.java
index 59a4e2c9..2a4649ee 100644
--- a/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/service/RelationService.java
+++ b/src/main/java/io/github/depromeet/knockknockbackend/domain/relation/service/RelationService.java
@@ -6,6 +6,7 @@
 import io.github.depromeet.knockknockbackend.domain.relation.exception.AlreadyFriendException;
 import io.github.depromeet.knockknockbackend.domain.relation.exception.AlreadySendRequestException;
 import io.github.depromeet.knockknockbackend.domain.relation.exception.FriendRequestNotFoundException;
+import io.github.depromeet.knockknockbackend.domain.relation.exception.NotFriendRelationException;
 import io.github.depromeet.knockknockbackend.domain.relation.presentation.dto.request.FriendRequest;
 import io.github.depromeet.knockknockbackend.domain.relation.presentation.dto.response.QueryFriendListResponse;
 import io.github.depromeet.knockknockbackend.domain.relation.presentation.dto.response.QueryFriendListResponseElement;
@@ -77,6 +78,14 @@ public HttpStatus sendFriendRequest(FriendRequest request) {
         return HttpStatus.CREATED;
     }
 
+    public void deleteRelation(FriendRequest request) {
+        if (!getIsFriend(request.getUserId())) {
+            throw NotFriendRelationException.EXCEPTION;
+        }
+
+        relationRepository.deleteById(getRelationId(request.getUserId()));
+    }
+
     public void acceptRequest(FriendRequest request) {
         updateIsFriendWithValidate(request, true);
     }
@@ -89,6 +98,10 @@ public boolean getIsFriend(Long userId) {
         return relationRepository.isFriend(SecurityUtils.getCurrentUserId(), userId);
     }
 
+    private Long getRelationId(Long userId) {
+        return relationRepository.getRelationIdByUserId(SecurityUtils.getCurrentUserId(), userId);
+    }
+
     private void updateIsFriendWithValidate(FriendRequest request, boolean isFriend) {
         if (!getIsFriend(request.getUserId())) {
             throw AlreadyFriendException.EXCEPTION;
diff --git a/src/main/java/io/github/depromeet/knockknockbackend/global/error/exception/ErrorCode.java b/src/main/java/io/github/depromeet/knockknockbackend/global/error/exception/ErrorCode.java
index 7a68a42a..e24d7277 100644
--- a/src/main/java/io/github/depromeet/knockknockbackend/global/error/exception/ErrorCode.java
+++ b/src/main/java/io/github/depromeet/knockknockbackend/global/error/exception/ErrorCode.java
@@ -28,6 +28,7 @@ public enum ErrorCode {
     ALREADY_SEND_REQUEST(400, "RELATION-400-1", "Already Send Request."),
     ALREADY_FRIEND_REQUEST(400, "RELATION-400-1", "Already Friend Request."),
     FRIEND_REQUEST_NOT_FOUND(404, "RELATION-404-1", "Friend Request Not Found."),
+    NOT_FRIEND_RELATION(404, "RELATION-404-2", "Not Friend Relation."),
 
     OPTION_NOT_FOUND(404, "OPTION-404-1", "Option Not Found."),
 
@@ -64,12 +65,16 @@ public enum ErrorCode {
     NOTIFICATION_FCM_FAIL_SEND(
             HttpStatus.INTERNAL_SERVER_ERROR.value(), "NOTIFICATION-500-1", "FCM ERROR"),
 
-    RESERVATION_NOT_FOUND(
-            HttpStatus.NOT_FOUND.value(), "RESERVATION-404-1", "Reservation Not Found"),
     RESERVATION_FORBIDDEN(
             HttpStatus.FORBIDDEN.value(),
             "RESERVATION-403-1",
             "The user has no access to the reservation"),
+    RESERVATION_ALREADY_EXIST(
+            HttpStatus.FORBIDDEN.value(),
+            "RESERVATION-403-2",
+            "The user already registered reservation"),
+    RESERVATION_NOT_FOUND(
+            HttpStatus.NOT_FOUND.value(), "RESERVATION-404-1", "Reservation Not Found"),
 
     STORAGE_FORBIDDEN(
             HttpStatus.FORBIDDEN.value(), "STORAGE-403-1", "The user has no access to the storage"),