A housing, a sun gear rotatably supported in the housing, a ring gear rotatably supported coaxially with the sun gear, a planetary carrier rotatably supported coaxially with the sun gear, a plurality of planetary gears rotatably supported to the planetary carrier and meshing with the sun gear and the ring gear, a motor connected to the ring gear to rotate the ring gear, an electromagnetic brake capable of applying a braking force to rotation of the sun gear, and an actuating member connected to the planetary carrier and linked to a door of a vehicle, and capable of moving the door in opening and closing directions are provided.