Upon a start of a release for releasing a braking state of a parking bake in a process of step 2, a control unit (13) performs hydraulic maintaining control by an ESC (11) in a subsequent step, step 3. As a result, a hydraulic pressure in a cylinder portion (46) increases according to a retraction of a piston (49) of a disk brake (41). If the control unit (13) determines in step 4 that the release of the parking brake has been completed, in step 5, the control unit (13) releases the hydraulic maintaining control by the ESC (11). The hydraulic pressure is temporarily increased in the cylinder portion (46) of the disk brake (41), thereby increasing an elastic deformation amount of a piston seal (56) to succeed in acquiring a sufficient rollback function.