Patent ID: 8272700

Claim:
A vehicle brake apparatus comprising: a boosted hydraulic pressure chamber; a master cylinder comprising: a master piston of which back side faces the boosted hydraulic pressure chamber; and a casing accommodating the master piston in a slidable manner; a hydraulic pressure generating source; a reservoir; and a pressure regulating valve unit which regulates output hydraulic pressure of the hydraulic pressure generating source in response to an input of brake application effort from a brake operation member for application to the boosted hydraulic pressure chamber; and a detection unit which detects an amount of the brake application effort of the brake operation member, wherein the master cylinder is connected to wheel brakes, in accordance with a detection value of the detection unit the pressure regulating valve unit is electrically driven to switch over following states of the vehicle brake apparatus: a state where the boosted hydraulic pressure chamber communicates with the hydraulic pressure generating source and the boosted hydraulic pressure chamber is separated from the reservoir; a state where the boosted hydraulic pressure chamber is separated from the hydraulic pressure generating source and the boosted pressure chamber communicates with the reservoir; and a state where the boosted hydraulic pressure chamber is separated from both the hydraulic pressure generating source and the reservoir; and wherein the master piston is formed into a stepped configuration, comprising: a larger diameter portion at front end; and a smaller diameter portion at a rear end corresponding to a side of the boosted hydraulic pressure chamber, the smaller diameter portion being slidable on a secondary bore cylinder.