the whole construction of the brake system is hereunder described in brief by reference to fig5 the brake system is designed to be executable a skid control or an abs control reference sign 1 shown in the drawing denotes a master cylinder capable of generating a brake fluid pressure when depressing a brake pedal 2 by a driver the master cylinder 1 is connected through a brake circuit 3 to wheel cylinders 4 4 serving as a brake actuating section in the drawing only two wheel brake cylinders are shown and the other two wheel brake cylinder connected to the brake circuit 3 are omitted for the purpose of illustrative simplicity additionally fluid pressure control valves 5 are disposed in the middle of the brake circuit 3 for reducing holding and building up the brake fluid pressure of the brake fluid in the wheel brake cylinder 4 a drain circuit 7 is connected to each of the fluid pressure control valves 5 for exhausting the brake fluid into a reservoir 6 during the pressure reduction operating mode a suction circuit 9 for a pump 8 is connected to the reservoir 6 whereas a discharge circuit 10 for the pump 8 is connected to a line closer to the master cylinder side which will be hereinafter referred to as an u201c upstream.