diff --git a/CHANGELOG.md b/CHANGELOG.md
index 464bdd677f..da005a60da 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -40,6 +40,7 @@
   (Cherry-picked from https://activitypub.software/TransFem-org/Sharkey/-/merge_requests/709)
 
 ### Misskey.js
+- Enhance: `/miauth/{sessionId}/check` の型を追加
 - Fix: Stream初期化時、別途WebSocketを指定する場合の型定義を修正
 
 ## 2024.10.1
diff --git a/packages/misskey-js/etc/misskey-js.api.md b/packages/misskey-js/etc/misskey-js.api.md
index 061b533b72..af73af080b 100644
--- a/packages/misskey-js/etc/misskey-js.api.md
+++ b/packages/misskey-js/etc/misskey-js.api.md
@@ -1160,6 +1160,13 @@ export type Endpoints = Overwrite<Endpoints_2, {
             };
         };
     };
+    'admin/roles/create': {
+        req: Overwrite<AdminRolesCreateRequest, {
+            policies: PartialRolePolicyOverride;
+        }>;
+        res: AdminRolesCreateResponse;
+    };
+}> & {
     'signup': {
         req: SignupRequest;
         res: SignupResponse;
@@ -1188,13 +1195,11 @@ export type Endpoints = Overwrite<Endpoints_2, {
             };
         };
     };
-    'admin/roles/create': {
-        req: Overwrite<AdminRolesCreateRequest, {
-            policies: PartialRolePolicyOverride;
-        }>;
-        res: AdminRolesCreateResponse;
+    [ep: `miauth/${string}/check`]: {
+        req: EmptyRequest;
+        res: MiAuthCheckResponse;
     };
-}>;
+};
 
 // @public (undocumented)
 type EndpointsResponse = operations['endpoints']['responses']['200']['content']['application/json'];
@@ -1223,6 +1228,7 @@ declare namespace entities {
         SigninWithPasskeyRequest,
         SigninWithPasskeyInitResponse,
         SigninWithPasskeyResponse,
+        MiAuthCheckResponse,
         PartialRolePolicyOverride,
         EmptyRequest,
         EmptyResponse,
@@ -2439,6 +2445,15 @@ type MetaRequest = operations['meta']['requestBody']['content']['application/jso
 // @public (undocumented)
 type MetaResponse = operations['meta']['responses']['200']['content']['application/json'];
 
+// @public (undocumented)
+type MiAuthCheckResponse = {
+    ok: true;
+    token: string;
+    user: UserDetailedNotMe;
+} | {
+    ok: false;
+};
+
 // @public (undocumented)
 type MiauthGenTokenRequest = operations['miauth___gen-token']['requestBody']['content']['application/json'];
 
diff --git a/packages/misskey-js/src/api.types.ts b/packages/misskey-js/src/api.types.ts
index 838949f8e1..c2cb55189f 100644
--- a/packages/misskey-js/src/api.types.ts
+++ b/packages/misskey-js/src/api.types.ts
@@ -1,6 +1,6 @@
 import { Endpoints as Gen } from './autogen/endpoint.js';
 import { UserDetailed } from './autogen/models.js';
-import { AdminRolesCreateRequest, AdminRolesCreateResponse, UsersShowRequest } from './autogen/entities.js';
+import { AdminRolesCreateRequest, AdminRolesCreateResponse, UsersShowRequest, EmptyRequest } from './autogen/entities.js';
 import {
 	PartialRolePolicyOverride,
 	SigninFlowRequest,
@@ -12,6 +12,7 @@ import {
 	SignupPendingResponse,
 	SignupRequest,
 	SignupResponse,
+	MiAuthCheckResponse,
 } from './entities.js';
 
 type Overwrite<T, U extends { [Key in keyof T]?: unknown }> = Omit<
@@ -57,6 +58,7 @@ export type SwitchCaseResponseType<E extends keyof Endpoints, P extends Endpoint
 export type Endpoints = Overwrite<
 	Gen,
 	{
+		// ▼ api.jsonのオーバーライド ▼
 		'users/show': {
 			req: UsersShowRequest;
 			res: {
@@ -70,40 +72,45 @@ export type Endpoints = Overwrite<
 				};
 			};
 		},
-		// api.jsonには載せないものなのでここで定義
-		'signup': {
-			req: SignupRequest;
-			res: SignupResponse;
-		},
-		// api.jsonには載せないものなのでここで定義
-		'signup-pending': {
-			req: SignupPendingRequest;
-			res: SignupPendingResponse;
-		},
-		// api.jsonには載せないものなのでここで定義
-		'signin-flow': {
-			req: SigninFlowRequest;
-			res: SigninFlowResponse;
-		},
-		'signin-with-passkey': {
-			req: SigninWithPasskeyRequest;
-			res: {
-				$switch: {
-					$cases: [
-						[
-							{
-								context: string;
-							},
-							SigninWithPasskeyResponse,
-						],
-					];
-					$default: SigninWithPasskeyInitResponse;
-				},
-			},
-		},
 		'admin/roles/create': {
 			req: Overwrite<AdminRolesCreateRequest, { policies: PartialRolePolicyOverride }>;
 			res: AdminRolesCreateResponse;
-		}
+		},
+		// ▲ api.jsonのオーバーライド ▲
 	}
->
+> & {
+	// ▼ api.jsonに載らないもの ▼
+	'signup': {
+		req: SignupRequest;
+		res: SignupResponse;
+	},
+	'signup-pending': {
+		req: SignupPendingRequest;
+		res: SignupPendingResponse;
+	},
+	'signin-flow': {
+		req: SigninFlowRequest;
+		res: SigninFlowResponse;
+	},
+	'signin-with-passkey': {
+		req: SigninWithPasskeyRequest;
+		res: {
+			$switch: {
+				$cases: [
+					[
+						{
+							context: string;
+						},
+						SigninWithPasskeyResponse,
+					],
+				];
+				$default: SigninWithPasskeyInitResponse;
+			},
+		},
+	},
+	[ep: `miauth/${string}/check`]: {
+		req: EmptyRequest;
+		res: MiAuthCheckResponse;
+	},
+	// ▲ api.jsonに載らないもの ▲
+};
diff --git a/packages/misskey-js/src/entities.ts b/packages/misskey-js/src/entities.ts
index dd88791ed0..5d6a139860 100644
--- a/packages/misskey-js/src/entities.ts
+++ b/packages/misskey-js/src/entities.ts
@@ -311,6 +311,14 @@ export type SigninWithPasskeyResponse = {
 	signinResponse: SigninFlowResponse & { finished: true };
 };
 
+export type MiAuthCheckResponse = {
+	ok: true;
+	token: string;
+	user: UserDetailedNotMe;
+} | {
+	ok: false;
+};
+
 type Values<T extends Record<PropertyKey, unknown>> = T[keyof T];
 
 export type PartialRolePolicyOverride = Partial<{[k in keyof RolePolicies]: Omit<Values<Role['policies']>, 'value'> & { value: RolePolicies[k] }}>;