PURPOSE: To reduce the liquid consumption on the front side in boosting, by installing a piston which is shifted in the boosting direction by receiving the brake hydraulic pressure of a rear brake piping system of a boosting cylinder device.

CONSTITUTION: A rear side brake pipe 31 and a conduit 34 (conduit which communicates to the accumulator 20A of an outside hydraulic source 20) which extends from a hydraulic type booster 14 are connected with the large diameter part 501 of a booster cylinder device 50, and a front side brake pipe 32 is connected with a small diameter part 502. Further, the rear side brake pipe 31 communicates to the rear side brake devices 41a and 41b, through a P valve 80 at the end part of the large diameter part 501, while the front side brake pipe 32 communicates to the front side brake devices 42a and 42b, passing through the small diameter part 502. Since the shift of a stepped piston is carried out by the brake hydraulic pressure of the rear side brake pipe 31, the necessity of increasing the stroke on the front side of a master ring 12 is obviated.