To suppress brake fluid accumulation within a reservoir by implementing pressure reducing control of a wheel cylinder via a pressure control means and by reducing boosting function of a brake boosting means in the case of being requested for reducing wheel cylinder pressure.

In the case deceleration of a wheel, for example a FR wheel, exceeds the second standard, a vacuum pressure control valve 23 is set to open position and an atmospheric pressure selector valve 29 is set to closed position so that the pressure differences with cylinders 13, 15 is reduced for reducing boosting function of a brake booster 5. At this time, the FR wheel is excepted from the object of boosting control and the brake booster 5 is operated based on a request from other wheels. At this stage, in order to control the hydraulic pressure of within the wheel cylinder 37 for the FR wheel, fluid pressure control valve 41 is set to closed position and fluid pressure control valve 42 is set to open position for discharging brake fluid within the wheel cylinder 37 and thereby to relieve the FR wheel of its locked condition.