To obtain a dummy reaction and a movement amount of a brake pedal which accord with a depressive force of the brake pedal even if a negative pressure of a constant pressure chamber varies, and to provide a more preferable brake feeling to a driver compared with conventional ones.
A brake reaction is not transmitted to brake pedal. Instead, a dummy reaction is transmitted to a valve plunger 17 and the brake pedal by dummy reaction applying means 41. An outer periphery of a valve body 5 on a rear side is surrounded by a cover 44, and a bellows 46 is provided over from the cover 44 to a retainer 33. An effective diameter of the bellows 46 is as same as diameters of a vacuum valve 24 and a relief valve 25. As a result, during operation of the brake power assist, a differential pressure between an air pressure within a variable pressure chamber B and an atmospheric pressure outside shells 1, 2 will not act on the valve body 5.
SAWADA MAMORU
IMOTO YUZO
DENSO CORP