An actuator includes: a fixed internal gear that is formed in an annular shape, has a tooth on an inner peripheral surface thereof, and is non-rotatably provided; a movable internal gear that is formed in an annular shape, has a tooth on an inner peripheral surface thereof, and is rotatably provided coaxially with the fixed internal gear; a plurality of external gears that mesh with the fixed internal gear and the movable internal gear, and rotate along an inner peripheral surface of the fixed internal gear; and a carrier that is formed in an annular shape, rotatably supports the external gears, has a tooth for receiving a turning force from a drive motor on an outer peripheral surface thereof, transmits a turning force from the drive motor to the external gears, and is rotatably provided coaxially with the movable internal gear.