The valve has disc-shaped valve body (1) with a fluid supply port (3) in the central portion thereof and composed of an elastic material whose peripheral portion is reinforced and fixed with a rigid material (2). The disc shaped valve body also has a thin walled portion in the intermediate annular portion between the fluid supply port and the peripheral portion in the radial direction, and/or an inflectional portion in the radial direction between the fluid supply port and the peripheral portion. The fluid supply port is closed when the valve body abuts against a fixed valve seat (4) placed so as to be opposite to the fluid supply port, and is opened when the valve body is separated from the fixed valve seat.
