To provide an air valve that can prevent external leakage of sanitary sewage and the like by reducing the frequency of opening and closing of a valve element and suppressing splash and dust scatter while maintaining an appreciable exhaust function.

The air valve comprises a valve casing 5 having a connection flange portion 1 for piping in a lower part and having a valve seat 4 in which an exhaust hole 3 is formed in an upper part, the valve element 6 for opening and closing the exhaust hole 3, a cover member 8 disposed over the valve casing 5 and provided with a pressure relief hole 8a, a diaphragm 7 for forming in the cover member 8 a pressure chamber 10 in communication with the atmosphere via the pressure relief hole a, a valve stem part 6a for connecting the valve element 6 and the diaphragm 7 and having a small diameter air hole 9 for interconnecting the pressure chamber 10 and the interior of the valve casing 5, a shaft 14 engaged at an elongate hole 12 with a pin 13 arranged at a lower end of the valve element 6 and suspended for vertical motion between a position to stop the small diameter air hole 9 and a position to open it, and a float 11 disposed in the valve casing 5 in a coupled relation to the shaft 14 to press the shaft 14 and the valve element 6 in the closing direction by means of buoyancy. The shaft 14 has a needle 18 reciprocated into and out of the small diameter air hole 9 to regulate an opening area of the small diameter air hole 9.