To adjust a vehicle height without any deterioration in safety of a vehicle by releasing braking force to front wheels and rear wheels by means of a parking brake forcibly releasing means in vehicle height adjustment under a braking force applied condition, in which braking force is applied to all the wheels by a parking braking means.

A parking brake forcibly releasing means 10 is added to a parking brake device, while relay valve 2, 13 are arranged independently on a rear side and on a front side. The parking brake forcibly releasing means 10 is constructed of a manual type on-off valve 11, a double check valve 12, the front side relay valve 13, and passages 1b2, 1b3 connecting these parts mutually. Therefore, while a parking brake is actuated, the manual type on-off valve 11 is opened so as to communicate the bypass passages 1b2, 1b3 to each other, so that pressurizing air is fed only to a chamber 4 on the rear side, and only the braking force to the rear wheel side is released when the parking brake is actuated. Then, a vehicle height is adjusted while the parking brake is applied to the front wheels.