A master cylinder comprising a large diameter pressurizing chamber and a small diameter hydraulic chamber, a control valve device in which a control valve body releases a hydraulic pressure in the large diameter pressurizing chamber to a reservoir side such that the hydraulic pressure in the large diameter pressurizing chamber is gradually reduced in accordance with a rise in a hydraulic pressure in the small hydraulic chamber, and a check valve device comprising a check valve chamber communicating with an relief passage, which releases a hydraulic pressure in the large diameter pressurizing chamber to the reservoir via the control valve device, and with a small diameter hydraulic chamber, respectively, and a check valve body accommodated in the check valve chamber for permitting flow of a brake fluid from the relief passage to the small hydraulic chamber, and for preventing flow of the brake fluid in a reverse direction.