diff --git a/README.md b/README.md
index 2eaeab0..c041158 100755
--- a/README.md
+++ b/README.md
@@ -68,6 +68,8 @@ pnpm i
 
 # 起動
 # (バックエンド/フロントエンドどちらもwatchします)
+# http://localhost:5173 (デフォルトのフロントエンド)にアクセスしてください
+# 開発環境のhttp://localhost:3300 (デフォルトのバックエンド)にはフロントエンド機能がありません
 pnpm run dev
 ```
 
diff --git a/packages/backend/src/modules/repositories/User.ts b/packages/backend/src/modules/repositories/User.ts
index 6496ee8..de28426 100644
--- a/packages/backend/src/modules/repositories/User.ts
+++ b/packages/backend/src/modules/repositories/User.ts
@@ -20,8 +20,11 @@ export class UserRepository extends EntityRepository<UserEntity> {
   async createUser(data: Pick<z.infer<typeof UserRepository.schema>, "userid" | "email" | "password" | "isAdmin"> & {
     invitationCode?: string;
   }) {
+    const isThisAdmin = (await this.em.count(UserEntity)) === 0
+      ? true
+      : false;
     const requiredInvitationCode = await this.em.getRepository(ConfigEntity).get("requiredInvitationCode", "true") as string;
-    if (requiredInvitationCode && !data.invitationCode) {
+    if (requiredInvitationCode && !data.invitationCode && !isThisAdmin) {
       return ErrorBase({
         bad: "client",
         code: "invitation_code_invalid",
diff --git a/packages/backend/src/routes/setup/create-admin.ts b/packages/backend/src/routes/setup/create-admin.ts
index ecf10b7..8af3650 100755
--- a/packages/backend/src/routes/setup/create-admin.ts
+++ b/packages/backend/src/routes/setup/create-admin.ts
@@ -3,7 +3,6 @@ import Logger from "@/lib/logger";
 import type { FastifyInstance } from "fastify";
 import { UserRepository } from "@/modules/repositories/User";
 import { DatabaseError, ErrorBase, InputError } from "@/errors";
-import { UniqueConstraintViolationException } from "@mikro-orm/core";
 
 export default function SetupCreateAdmin(fastify: FastifyInstance) {
   const logger = new Logger("Endpoint | setup/create-admin");
@@ -27,8 +26,8 @@ export default function SetupCreateAdmin(fastify: FastifyInstance) {
       if (userCount > 0) {
         return res.code(409).send(ErrorBase({
           bad: "client",
-          code: "first_admin_already_exists",
-          message: "最初の管理者ユーザーは既に存在します。",
+          code: "admin_already_exists",
+          message: "管理者ユーザーは既に存在します。",
         }));
       } 
     } catch (err) {
@@ -38,12 +37,16 @@ export default function SetupCreateAdmin(fastify: FastifyInstance) {
     }
 
     try {
-      await fastify.orm.em.getRepository(UserEntity).createUser({
+      const error = await fastify.orm.em.getRepository(UserEntity).createUser({
         ...result.data,
         isAdmin: true,
       });
 
-      logger.warn("First administrator account has been created.");
+      if (error) {
+        return res.code(400).send(error);
+      }
+
+      logger.warn("Administrator account has been created.");
 
       return res.code(200).send({
         success: true,
diff --git a/packages/frontend/src/components/Textarea.vue b/packages/frontend/src/components/Textarea.vue
index 61af609..2764c13 100644
--- a/packages/frontend/src/components/Textarea.vue
+++ b/packages/frontend/src/components/Textarea.vue
@@ -34,6 +34,10 @@
   color: var(--text-color);
   font-size: 1rem;
   border: 1px solid transparent;
+  width: 100%;
+  max-height: 20rem;
+  box-sizing: border-box;
+  resize: none;
   outline: none;
   padding: 0.6rem;
   border-radius: 0.25rem;