When an EPB performs a locking operation of operating a parking brake, a pressure-decreasing limit control is performed until a driving shaft contacts a piston. Accordingly, even when the time of decreasing the W/C pressure by a service brake is equal to the time of brining the driving shaft having moved by the motor driving of the EPB into contact with the piston are equal to each other, it is possible to prevent the piston, which has been urged to the driving shaft with the decreasing of the W/C pressure, from colliding with the driving shaft with a great impact, thereby preventing a large load from being applied to the driving shaft.