Patent ID: 8256216

Claim:
A vehicular brake apparatus comprising: a master cylinder comprising: a casing; and a master piston of which rear face faces a boosted hydraulic pressure application chamber and which is slidably accommodated in the casing; a hydraulic pressure source capable of generating hydraulic pressure regardless of an operation of a brake operation member; and a hydraulic pressure booster comprising: a backup piston which is slidably fitted into the casing while a front face thereof facing the boosted hydraulic pressure application chamber and a retraction limit thereof is restricted; a pressure regulator built into the backup piston and being capable of adjusting the hydraulic pressure output from the hydraulic pressure source and applying the hydraulic pressure to the boosted hydraulic pressure application chamber; and a control piston operating to balance reaction force due to the hydraulic pressure of the boosted hydraulic pressure application chamber with braking operation force of the brake operation member and to enable the pressure regulator to perform pressure adjustment, wherein the backup piston moves forward to directly push the master piston against the hydraulic pressure force due to the hydraulic pressure output from the hydraulic pressure source as the brake operation force is transmitted from the control piston to the backup piston when the hydraulic pressure of the boosted hydraulic pressure application chamber is low, wherein an input-side annular chamber connected to the hydraulic pressure source is provided between the casing and the backup piston, an annular sealing member which seals between the boosted hydraulic pressure application chamber and the input-side annular chamber is disposed between the casing and the backup piston, and a communication passage is provided in one of the backup piston and the casing, and the communication passage communicates the input-side annular chamber with the boosted hydraulic pressure application chamber as the backup piston moves forward by a predetermined stroke or more so as to directly push the master piston.