Automotive hydraulic pressure brake system

Automotive hydraulic pressure brake system with a stroke simulator (4) is proposed which while the electric control system is functioning properly, the supply of hydraulic pressure from a master cylinder (1) is cut off and hydraulic pressure is generated by a power pump (7). This improves response upon rapid pressure increase while minimizing the increase of pedal stroke and the worsening of the pedal feeling. A bypass (19) is provided to communicate the master cylinder (1) to the wheel cylinders (2A,2B) while bypassing an on-off valve (3) to be closed during ordinary braking. A shut-off valve (21) is provided in the bypass (19) and a check valve (20) or a relief valve for allowing only a fluid flow from the master cylinder (1) toward the wheel brake cylinders (2A,2B) is provided.