diff --git a/src/client/init.ts b/src/client/init.ts
index 123d4020e..654e17639 100644
--- a/src/client/init.ts
+++ b/src/client/init.ts
@@ -37,6 +37,8 @@ import { isMobile } from '@client/scripts/is-mobile';
 import { initializeSw } from '@client/scripts/initialize-sw';
 import { reloadChannel } from '@client/scripts/unison-reload';
 import { reactionPicker } from '@client/scripts/reaction-picker';
+import { getUrlWithoutLoginId } from '@client/scripts/login-id';
+import { getAccountFromId } from '@client/scripts/get-account-from-id';
 
 console.info(`Misskey v${version}`);
 
@@ -116,6 +118,25 @@ const html = document.documentElement;
 html.setAttribute('lang', lang);
 //#endregion
 
+//#region loginId
+const params = new URLSearchParams(location.search);
+const loginId = params.get('loginId');
+
+if (loginId) {
+	const target = getUrlWithoutLoginId(location.href);
+
+	if (!$i || $i.id !== loginId) {
+		const account = await getAccountFromId(loginId);
+		if (account) {
+			await login(account.token, target);
+		}
+	}
+
+	history.replaceState({ misskey: 'loginId' }, '', target);
+}
+
+//#endregion
+
 //#region Fetch user
 if ($i && $i.token) {
 	if (_DEV_) {
diff --git a/src/client/scripts/login-id.ts b/src/client/scripts/login-id.ts
new file mode 100644
index 000000000..0f9c6be4a
--- /dev/null
+++ b/src/client/scripts/login-id.ts
@@ -0,0 +1,11 @@
+export function getUrlWithLoginId(url: string, loginId: string) {
+	const u = new URL(url, origin);
+	u.searchParams.append('loginId', loginId);
+	return u.toString();
+}
+
+export function getUrlWithoutLoginId(url: string) {
+	const u = new URL(url);
+	u.searchParams.delete('loginId');
+	return u.toString();
+}