A rotation of a right wheel (3RR) and a rotation of a left wheel (3RL) of a vehicle are locked respectively by independent parking lock mechanisms (6). Each parking lock mechanism (6) comprises a locking operation prevention mechanism (63c,63d) which mechanically prevents the locking operation of the parking lock mechanism (6) when a wheel rotation speed exceeds a predetermined parking lock prevention wheel rotation speed. The controller (CU, 10) is programmed to prevent the locking operation of the parking lock mechanisms (6) of the right and left wheels (3RR, 3RL) when a predetermined parking lock permitting condition based on wheel rotation speeds of the right wheel (3RR) and the left wheel (3RL) is not satisfied, thereby preventing a state in which one of the right and left wheels (3RR, 3RL) is prevented from rotating while the other is not prevented from rotating.