diff --git a/src/group/group.service.ts b/src/group/group.service.ts
index 6495259..8ce3051 100644
--- a/src/group/group.service.ts
+++ b/src/group/group.service.ts
@@ -44,26 +44,13 @@ export class GroupService {
     return this.groupRepository.delete(groupId);
   }
 
-  async deleteMember(groupId: string, memberId: string): Promise<void> {
-    const group = (await this.groupRepository.findOne(groupId)) as Group;
-    if (group.members.includes(memberId)) {
-      group.members = group.members.filter((member) => member !== memberId);
-    }
-    await this.groupRepository.update(groupId, group);
-  }
-
   async deleteMembers(groupId: string, memberIds: string[]): Promise<void> {
     const group = (await this.groupRepository.findOne(groupId)) as Group;
     const groupMembers = group.members;
 
-    if (
-      Array.isArray(memberIds) &&
-      memberIds.every((item) => typeof item === 'string')
-    ) {
-      group.members = groupMembers.filter(
-        (member) => !memberIds.includes(member),
-      );
-    }
+    group.members = groupMembers.filter(
+      (member) => !memberIds.find((id) => id === member),
+    );
 
     await this.groupRepository.update(groupId, group);
   }
diff --git a/src/member/member.service.ts b/src/member/member.service.ts
index f946223..74ec67b 100644
--- a/src/member/member.service.ts
+++ b/src/member/member.service.ts
@@ -70,11 +70,10 @@ export class MemberService {
   }
 
   async delete(groupId: string, memberId: string): Promise<void> {
-    const memberIds: string[] = [memberId];
-    if (!this.validateMemberIds(memberIds)) throw new NotFoundException();
+    if (!this.validateMemberIds([memberId])) throw new NotFoundException();
 
-    this.memberRepository.delete(memberIds);
-    await this.groupService.deleteMember(groupId, memberId);
+    this.memberRepository.delete([memberId]);
+    await this.groupService.deleteMembers(groupId, [memberId]);
   }
 
   async deleteGroupMembers(