To provide an air valve that can prevent an external outflow of liquid even if an exhaust hole is in a state incapable of full closing because of an effect of a foreign matter such as dust.

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 the exhaust hole 3 is formed in an upper part, a valve element 6 for opening and closing the exhaust hole 3, and a float 11 disposed in the valve casing to press the valve element 6 in the closing direction by means of buoyancy. A spray guard 15 having vents 15a is disposed under the valve element 6, and an auxiliary float 20 for opening and closing the vents 15a is disposed just under the spray guard 15. The auxiliary float 20 has a downwardly projecting skirt portion 20A on an outer circumferential portion.