diff --git a/locales/ja.yml b/locales/ja.yml
index 84694e3c7..4d4c85362 100644
--- a/locales/ja.yml
+++ b/locales/ja.yml
@@ -148,7 +148,7 @@ common:
       unavailable: "既に利用されています"
       error: "通信エラー"
       invalid-format: "a~z、A~Z、0~9、_が使えます"
-      too-short: "3文字以上でお願いします！"
+      too-short: "1文字以上でお願いします！"
       too-long: "20文字以内でお願いします"
       password: "パスワード"
       password-placeholder: "8文字以上を推奨します"
diff --git a/src/client/app/common/views/components/signup.vue b/src/client/app/common/views/components/signup.vue
index 8d0b16cab..30fe7b7ad 100644
--- a/src/client/app/common/views/components/signup.vue
+++ b/src/client/app/common/views/components/signup.vue
@@ -2,7 +2,7 @@
 <form class="mk-signup" @submit.prevent="onSubmit" autocomplete="off">
 	<label class="username">
 		<p class="caption">%fa:at%%i18n:common.tags.mk-signup.username%</p>
-		<input v-model="username" type="text" pattern="^[a-zA-Z0-9_]{3,20}$" placeholder="a~z、A~Z、0~9、-" autocomplete="off" required @input="onChangeUsername"/>
+		<input v-model="username" type="text" pattern="^[a-zA-Z0-9_]{1,20}$" placeholder="a~z、A~Z、0~9、-" autocomplete="off" required @input="onChangeUsername"/>
 		<p class="profile-page-url-preview" v-if="shouldShowProfileUrl">{{ `${url}/@${username}` }}</p>
 		<p class="info" v-if="usernameState == 'wait'" style="color:#999">%fa:spinner .pulse .fw%%i18n:common.tags.mk-signup.checking%</p>
 		<p class="info" v-if="usernameState == 'ok'" style="color:#3CB7B5">%fa:check .fw%%i18n:common.tags.mk-signup.available%</p>
diff --git a/src/client/app/dev/views/new-app.vue b/src/client/app/dev/views/new-app.vue
index 2317f24d4..a3d7af4b9 100644
--- a/src/client/app/dev/views/new-app.vue
+++ b/src/client/app/dev/views/new-app.vue
@@ -6,13 +6,13 @@
 				<b-form-input v-model="name" type="text" placeholder="ex) Misskey for iOS" autocomplete="off" required/>
 			</b-form-group>
 			<b-form-group label="ID" description="あなたのアプリのID。">
-				<b-input v-model="nid" type="text" pattern="^[a-zA-Z0-9_]{3,30}$" placeholder="ex) misskey-for-ios" autocomplete="off" required/>
+				<b-input v-model="nid" type="text" pattern="^[a-zA-Z0-9_]{1,30}$" placeholder="ex) misskey-for-ios" autocomplete="off" required/>
 				<p class="info" v-if="nidState == 'wait'" style="color:#999">%fa:spinner .pulse .fw%確認しています...</p>
 				<p class="info" v-if="nidState == 'ok'" style="color:#3CB7B5">%fa:fw check%利用できます</p>
 				<p class="info" v-if="nidState == 'unavailable'" style="color:#FF1161">%fa:fw exclamation-triangle%既に利用されています</p>
 				<p class="info" v-if="nidState == 'error'" style="color:#FF1161">%fa:fw exclamation-triangle%通信エラー</p>
 				<p class="info" v-if="nidState == 'invalid-format'" style="color:#FF1161">%fa:fw exclamation-triangle%a~z、A~Z、0~9、_が使えます</p>
-				<p class="info" v-if="nidState == 'min-range'" style="color:#FF1161">%fa:fw exclamation-triangle%3文字以上でお願いします！</p>
+				<p class="info" v-if="nidState == 'min-range'" style="color:#FF1161">%fa:fw exclamation-triangle%1文字以上でお願いします！</p>
 				<p class="info" v-if="nidState == 'max-range'" style="color:#FF1161">%fa:fw exclamation-triangle%30文字以内でお願いします</p>
 			</b-form-group>
 			<b-form-group label="アプリの概要" description="あなたのアプリの簡単な説明や紹介。">
diff --git a/src/models/app.ts b/src/models/app.ts
index 703f4ef8f..446f0c62f 100644
--- a/src/models/app.ts
+++ b/src/models/app.ts
@@ -24,7 +24,7 @@ export type IApp = {
 };
 
 export function isValidNameId(nameId: string): boolean {
-	return typeof nameId == 'string' && /^[a-zA-Z0-9_]{3,30}$/.test(nameId);
+	return typeof nameId == 'string' && /^[a-zA-Z0-9_]{1,30}$/.test(nameId);
 }
 
 /**
diff --git a/src/models/user.ts b/src/models/user.ts
index 36c63a56d..b05bb8812 100644
--- a/src/models/user.ts
+++ b/src/models/user.ts
@@ -89,7 +89,7 @@ export const isRemoteUser = (user: any): user is IRemoteUser =>
 
 //#region Validators
 export function validateUsername(username: string): boolean {
-	return typeof username == 'string' && /^[a-zA-Z0-9_]{3,20}$/.test(username);
+	return typeof username == 'string' && /^[a-zA-Z0-9_]{1,20}$/.test(username);
 }
 
 export function validatePassword(password: string): boolean {