PURPOSE: To obtain a simple structure by installing a valve body made of the soft elastic material having a specific gravity of 0.95 or less in a cylindrical valve chamber having an air discharge passage on the upper bottom of a valve seat and a fluid inflow passage on the lower bottom.

CONSTITUTION: The upper bottom 1b of a valve chamber 1a is formed into conical form, and a gas flow-out passage 1c is formed, and the upper surface 2b of a basic body 2 constitutes the bottom surface of the valve chamber 1a, and a fluid inflow passage 2c penetrates. A spherical valve body 3 is mace of rubber elastic material, and the specific gravity is set 0.95 or less. Therefore, the valve body is press-attached onto the upper bottom by the liquid pressure, and the liquid is prevented from being discharged from the gas discharge passage, and the simple constitution is obtained, and the sure operation is permitted.