diff --git a/CHANGELOG.md b/CHANGELOG.md
index cfc07476e0..8f0fd24c44 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,7 +1,7 @@
 ## Unreleased
 
 ### General
--
+- Enhance: セキュリティ向上のため、サインイン時もCAPTCHAを求めるようになりました
 
 ### Client
 - Enhance: フォロワーへのメッセージ欄のデザイン改良
diff --git a/packages/backend/src/server/api/SigninApiService.ts b/packages/backend/src/server/api/SigninApiService.ts
index edac9b3beb..2ccc75da00 100644
--- a/packages/backend/src/server/api/SigninApiService.ts
+++ b/packages/backend/src/server/api/SigninApiService.ts
@@ -9,6 +9,7 @@ import * as OTPAuth from 'otpauth';
 import { IsNull } from 'typeorm';
 import { DI } from '@/di-symbols.js';
 import type {
+	MiMeta,
 	SigninsRepository,
 	UserProfilesRepository,
 	UsersRepository,
@@ -20,6 +21,8 @@ import { IdService } from '@/core/IdService.js';
 import { bindThis } from '@/decorators.js';
 import { WebAuthnService } from '@/core/WebAuthnService.js';
 import { UserAuthService } from '@/core/UserAuthService.js';
+import { CaptchaService } from '@/core/CaptchaService.js';
+import { FastifyReplyError } from '@/misc/fastify-reply-error.js';
 import { RateLimiterService } from './RateLimiterService.js';
 import { SigninService } from './SigninService.js';
 import type { AuthenticationResponseJSON } from '@simplewebauthn/types';
@@ -31,6 +34,9 @@ export class SigninApiService {
 		@Inject(DI.config)
 		private config: Config,
 
+		@Inject(DI.meta)
+		private meta: MiMeta,
+
 		@Inject(DI.usersRepository)
 		private usersRepository: UsersRepository,
 
@@ -45,6 +51,7 @@ export class SigninApiService {
 		private signinService: SigninService,
 		private userAuthService: UserAuthService,
 		private webAuthnService: WebAuthnService,
+		private captchaService: CaptchaService,
 	) {
 	}
 
@@ -56,6 +63,10 @@ export class SigninApiService {
 				password: string;
 				token?: string;
 				credential?: AuthenticationResponseJSON;
+				'hcaptcha-response'?: string;
+				'g-recaptcha-response'?: string;
+				'turnstile-response'?: string;
+				'm-captcha-response'?: string;
 			};
 		}>,
 		reply: FastifyReply,
@@ -139,6 +150,32 @@ export class SigninApiService {
 		};
 
 		if (!profile.twoFactorEnabled) {
+			if (process.env.NODE_ENV !== 'test') {
+				if (this.meta.enableHcaptcha && this.meta.hcaptchaSecretKey) {
+					await this.captchaService.verifyHcaptcha(this.meta.hcaptchaSecretKey, body['hcaptcha-response']).catch(err => {
+						throw new FastifyReplyError(400, err);
+					});
+				}
+
+				if (this.meta.enableMcaptcha && this.meta.mcaptchaSecretKey && this.meta.mcaptchaSitekey && this.meta.mcaptchaInstanceUrl) {
+					await this.captchaService.verifyMcaptcha(this.meta.mcaptchaSecretKey, this.meta.mcaptchaSitekey, this.meta.mcaptchaInstanceUrl, body['m-captcha-response']).catch(err => {
+						throw new FastifyReplyError(400, err);
+					});
+				}
+
+				if (this.meta.enableRecaptcha && this.meta.recaptchaSecretKey) {
+					await this.captchaService.verifyRecaptcha(this.meta.recaptchaSecretKey, body['g-recaptcha-response']).catch(err => {
+						throw new FastifyReplyError(400, err);
+					});
+				}
+
+				if (this.meta.enableTurnstile && this.meta.turnstileSecretKey) {
+					await this.captchaService.verifyTurnstile(this.meta.turnstileSecretKey, body['turnstile-response']).catch(err => {
+						throw new FastifyReplyError(400, err);
+					});
+				}
+			}
+
 			if (same) {
 				return this.signinService.signin(request, reply, user);
 			} else {
diff --git a/packages/frontend/src/components/MkSignin.vue b/packages/frontend/src/components/MkSignin.vue
index 7942a84d66..8ebdac0220 100644
--- a/packages/frontend/src/components/MkSignin.vue
+++ b/packages/frontend/src/components/MkSignin.vue
@@ -32,7 +32,11 @@ SPDX-License-Identifier: AGPL-3.0-only
 				<template #prefix><i class="ti ti-lock"></i></template>
 				<template #caption><button class="_textButton" type="button" @click="resetPassword">{{ i18n.ts.forgotPassword }}</button></template>
 			</MkInput>
-			<MkButton type="submit" large primary rounded :disabled="signing" style="margin: 0 auto;">{{ signing ? i18n.ts.loggingIn : i18n.ts.login }}</MkButton>
+			<MkCaptcha v-if="instance.enableHcaptcha" ref="hcaptcha" v-model="hCaptchaResponse" :class="$style.captcha" provider="hcaptcha" :sitekey="instance.hcaptchaSiteKey"/>
+			<MkCaptcha v-if="instance.enableMcaptcha" ref="mcaptcha" v-model="mCaptchaResponse" :class="$style.captcha" provider="mcaptcha" :sitekey="instance.mcaptchaSiteKey" :instanceUrl="instance.mcaptchaInstanceUrl"/>
+			<MkCaptcha v-if="instance.enableRecaptcha" ref="recaptcha" v-model="reCaptchaResponse" :class="$style.captcha" provider="recaptcha" :sitekey="instance.recaptchaSiteKey"/>
+			<MkCaptcha v-if="instance.enableTurnstile" ref="turnstile" v-model="turnstileResponse" :class="$style.captcha" provider="turnstile" :sitekey="instance.turnstileSiteKey"/>
+			<MkButton type="submit" large primary rounded :disabled="captchaFailed || signing" style="margin: 0 auto;">{{ signing ? i18n.ts.loggingIn : i18n.ts.login }}</MkButton>
 		</div>
 		<div v-if="totpLogin" class="2fa-signin" :class="{ securityKeys: user && user.securityKeys }">
 			<div v-if="user && user.securityKeys" class="twofa-group tap-group">
@@ -68,7 +72,7 @@ SPDX-License-Identifier: AGPL-3.0-only
 </template>
 
 <script lang="ts" setup>
-import { defineAsyncComponent, ref } from 'vue';
+import { computed, defineAsyncComponent, ref } from 'vue';
 import { toUnicode } from 'punycode/';
 import * as Misskey from 'misskey-js';
 import { supported as webAuthnSupported, get as webAuthnRequest, parseRequestOptionsFromJSON } from '@github/webauthn-json/browser-ponyfill';
@@ -85,6 +89,8 @@ import * as os from '@/os.js';
 import { misskeyApi } from '@/scripts/misskey-api.js';
 import { login } from '@/account.js';
 import { i18n } from '@/i18n.js';
+import { instance } from '@/instance.js';
+import MkCaptcha, { type Captcha } from '@/components/MkCaptcha.vue';
 
 const signing = ref(false);
 const user = ref<Misskey.entities.UserDetailed | null>(null);
@@ -98,6 +104,22 @@ const isBackupCode = ref(false);
 const queryingKey = ref(false);
 let credentialRequest: CredentialRequestOptions | null = null;
 const passkey_context = ref('');
+const hcaptcha = ref<Captcha | undefined>();
+const mcaptcha = ref<Captcha | undefined>();
+const recaptcha = ref<Captcha | undefined>();
+const turnstile = ref<Captcha | undefined>();
+const hCaptchaResponse = ref<string | null>(null);
+const mCaptchaResponse = ref<string | null>(null);
+const reCaptchaResponse = ref<string | null>(null);
+const turnstileResponse = ref<string | null>(null);
+
+const captchaFailed = computed((): boolean => {
+	return (
+		instance.enableHcaptcha && !hCaptchaResponse.value ||
+		instance.enableMcaptcha && !mCaptchaResponse.value ||
+		instance.enableRecaptcha && !reCaptchaResponse.value ||
+		instance.enableTurnstile && !turnstileResponse.value);
+});
 
 const emit = defineEmits<{
 	(ev: 'login', v: any): void;
@@ -227,6 +249,10 @@ function onSubmit(): void {
 		misskeyApi('signin', {
 			username: username.value,
 			password: password.value,
+			'hcaptcha-response': hCaptchaResponse.value,
+			'm-captcha-response': mCaptchaResponse.value,
+			'g-recaptcha-response': reCaptchaResponse.value,
+			'turnstile-response': turnstileResponse.value,
 			token: user.value?.twoFactorEnabled ? token.value : undefined,
 		}).then(res => {
 			emit('login', res);
@@ -236,6 +262,11 @@ function onSubmit(): void {
 }
 
 function loginFailed(err: any): void {
+	hcaptcha.value?.reset?.();
+	mcaptcha.value?.reset?.();
+	recaptcha.value?.reset?.();
+	turnstile.value?.reset?.();
+
 	switch (err.id) {
 		case '6cc579cc-885d-43d8-95c2-b8c7fc963280': {
 			os.alert({
diff --git a/packages/frontend/src/components/MkSignupDialog.form.vue b/packages/frontend/src/components/MkSignupDialog.form.vue
index 4ab4380ad5..38cac7f644 100644
--- a/packages/frontend/src/components/MkSignupDialog.form.vue
+++ b/packages/frontend/src/components/MkSignupDialog.form.vue
@@ -81,10 +81,10 @@ SPDX-License-Identifier: AGPL-3.0-only
 import { ref, computed } from 'vue';
 import { toUnicode } from 'punycode/';
 import * as Misskey from 'misskey-js';
+import * as config from '@@/js/config.js';
 import MkButton from './MkButton.vue';
 import MkInput from './MkInput.vue';
 import MkCaptcha, { type Captcha } from '@/components/MkCaptcha.vue';
-import * as config from '@@/js/config.js';
 import * as os from '@/os.js';
 import { misskeyApi } from '@/scripts/misskey-api.js';
 import { login } from '@/account.js';
@@ -105,6 +105,7 @@ const emit = defineEmits<{
 const host = toUnicode(config.host);
 
 const hcaptcha = ref<Captcha | undefined>();
+const mcaptcha = ref<Captcha | undefined>();
 const recaptcha = ref<Captcha | undefined>();
 const turnstile = ref<Captcha | undefined>();
 
@@ -281,6 +282,7 @@ async function onSubmit(): Promise<void> {
 	} catch {
 		submitting.value = false;
 		hcaptcha.value?.reset?.();
+		mcaptcha.value?.reset?.();
 		recaptcha.value?.reset?.();
 		turnstile.value?.reset?.();