In a system including a reservoir tank RSV integral with a master cylinder M/C, an inlet fluid passage 16 for connecting an inlet portion 22 of a pump P to the reservoir tank RSV, a pressure reducing fluid passage 32 that connects the inlet fluid passage 16 to wheel cylinders W/C and a normally closed pressure reducing vale 30 that is connected to the pressure reducing fluid passage 32 and opened when it is intended to depressurize a brake fluid to in the wheel cylinders thereby to return the brake fluid to the reservoir tank through the inlet fluid passage 16, there is employed a normally closed reservoir shutting valve 31 that is connected to the pressure reducing valve 30 in series with respect to the wheel cylinders W/C and the reservoir tank RSV.