To provide an air valve which makes possible intake and exhaust of air in large quantities as well as its smooth operation.

Valve bodies 27a, 27b mounted on a common valve stem 28 are arranged in a valve chamber 20, and the interior of float chamber 10 is isolated mechanically from an intake/exhaust port 40 by bringing the valve bodies into meeting contacts with valve seats 25a, 25b with said valve stem 28 being actuated by a spring 30 upward. When the float chamber is not filled with water, then the valves are released under the action of dead weight of a float 11, while the valves are closed as the float is lifted due to filling by water. Under the closed conditions, as the air in the filled water is accumulated in the upper portion of the float chamber and in the valve chamber, the float is moved downward with a lowering of water level, and eventually the dead weight of the float acts on the valve stem causing both of the valves with a lowering of the float to move downward against the spring force, leading to valve opening and air intake/exhaust. When a seal 13 of the float is brought into meeting contact with a valve seat 21 with the lift of the float, the float chamber and the exhaust part are isolated to each other, and no water leakage is possible, even if any problem happens to the sealing action between the valve bodies 27a, 27b and the valve seats 25a, 25b.