In case of power supply loss, a parking lock is operated by moving a piston of a hydraulic actuator rightward by use of hydraulic pressure accumulated in an accumulator. If a hydraulic pressure generating source becomes unable to generate line pressure due to its failure after the power supply loss, it is desirable that the parking lock be releasable to tow a vehicle, for example. In that time, because the hydraulic pressure in the accumulator has got out via an orifice, the parking lock can be released by moving the piston in the hydraulic actuator leftward by use of a manual operation device without interruption by the hydraulic pressure accumulated in the accumulator. Because the hydraulic pressure in the accumulator is automatically released via the orifice, a complicated mechanism for enabling the manual operation device to work without interference from the hydraulic actuator becomes unnecessary.