An actuator may include a motor generating a rotational force, a gear assembly transmitting the rotational force of the motor, and a housing accommodating the gear assembly therein. The gear assembly includes a driving gear provided on a driving shaft of the motor, a first gear unit connected with the driving gear, and a second gear unit connected with the first gear unit to transmit the rotational force transmitted from the first gear unit to a power conversion unit, and the first gear unit includes a gear shaft, a first driven gear provided on one side of the gear shaft and meshed with the driving gear, a second driven gear provided on the other side of the gear shaft and meshed with the second gear unit, and a bearing provided on the gear shaft between the first driven gear and the second driven gear.