diff --git a/dictation_server/src/features/users/test/users.service.mock.ts b/dictation_server/src/features/users/test/users.service.mock.ts
index a59284a..803014e 100644
--- a/dictation_server/src/features/users/test/users.service.mock.ts
+++ b/dictation_server/src/features/users/test/users.service.mock.ts
@@ -20,6 +20,7 @@ export type UsersRepositoryMockValue = {
   findUserById: User | Error;
   createNormalUser: User | Error;
   findSameAccountUsers: User[] | Error;
+  findUserByExternalId: User | Error;
 };
 
 export type AdB2cMockValue = {
@@ -186,6 +187,7 @@ export const makeUsersRepositoryMock = (value: UsersRepositoryMockValue) => {
     findUserById,
     createNormalUser,
     findSameAccountUsers,
+    findUserByExternalId,
   } = value;
 
   const aIdError = new authorIdError('ER_DUP_ENTRY');
@@ -213,6 +215,10 @@ export const makeUsersRepositoryMock = (value: UsersRepositoryMockValue) => {
         : jest
             .fn<Promise<User[] | undefined>, []>()
             .mockResolvedValue(findSameAccountUsers),
+    findUserByExternalId:
+      findUserByExternalId instanceof Error
+        ? jest.fn<Promise<void>, []>().mockRejectedValue(findUserByExternalId)
+        : jest.fn<Promise<User>, []>().mockResolvedValue(findUserByExternalId),
   };
 };
 
@@ -325,5 +331,6 @@ export const makeDefaultUsersRepositoryMockValue =
       findUserById: newUser,
       createNormalUser: newUser,
       findSameAccountUsers: [user1, user2],
+      findUserByExternalId: newUser,
     };
   };
diff --git a/dictation_server/src/features/users/users.service.ts b/dictation_server/src/features/users/users.service.ts
index 317a006..4c96728 100644
--- a/dictation_server/src/features/users/users.service.ts
+++ b/dictation_server/src/features/users/users.service.ts
@@ -98,12 +98,13 @@ export class UsersService {
     //アクセストークンからユーザーIDを取得する
     // TODO アクセストークンの中身が具体的に確定したら、型変換を取り払う必要があるかも
     this.logger.log(`[IN] ${this.createUser.name}`);
-    const userId = Number(accessToken.userId);
 
     //DBよりアクセス者の所属するアカウントIDを取得する
     let adminUser: EntityUser;
     try {
-      adminUser = await this.usersRepository.findUserById(userId);
+      adminUser = await this.usersRepository.findUserByExternalId(
+        accessToken.userId,
+      );
     } catch (e) {
       throw new HttpException(
         makeErrorResponse('E009999'),
@@ -281,7 +282,7 @@ export class UsersService {
 
       // DBから同一アカウントのユーザ一覧を取得する
       const dbUsers = await this.usersRepository.findSameAccountUsers(
-        Number(payload.userId),
+        payload.userId,
       );
 
       // 値をマージして定義されたレスポンス通りに返す
diff --git a/dictation_server/src/repositories/users/users.repository.service.ts b/dictation_server/src/repositories/users/users.repository.service.ts
index 8617df0..6e7bdb5 100644
--- a/dictation_server/src/repositories/users/users.repository.service.ts
+++ b/dictation_server/src/repositories/users/users.repository.service.ts
@@ -165,17 +165,19 @@ export class UsersRepositoryService {
 
   /**
    * 同じアカウントIDを持つユーザーを探す
-   * @param userId
+   * @param criteria
    * @returns User[]
    */
-  async findSameAccountUsers(userId: number): Promise<User[]> {
-    const dbUser = await this.dataSource
-      .getRepository(User)
-      .findOne({ where: [{ id: userId }] });
+  async findSameAccountUsers(criteria: string): Promise<User[]> {
+    const dbUser = await this.dataSource.getRepository(User).findOne({
+      where: {
+        external_id: criteria,
+      },
+    });
 
     const dbUsers = await this.dataSource
       .getRepository(User)
-      .find({ where: [{ account_id: dbUser.account_id }] });
+      .find({ where: { account_id: dbUser.account_id } });
 
     return dbUsers;
   }