A pressure control reservoir for a vehicle brake system is disposed in a hydraulic line extending from a master cylinder to a wheel cylinder through a pump. The pressure control reservoir includes a check valve which consists of a valve seat and a valve. The check valve is closed when an excessive pressure of brake fluid produced by the master cylinder. The valve is stationary. The valve seat is moved in response to an elevated level of the pressure of brake fluid into engagement with the valve, so that the check valve is closed. With these arrangements, the check valve is closed before a piston starts to move to change the volume of a reservoir chamber, thus permitting the volume of the brake fluid required to close the check valve to be decreased, which minimizes the uncomfortable feeling given to a driver of the vehicle when actuating the brakes.