To provide an air valve provided with a level gauge by which the state of operation can be easily recognized only by visual observation.

In the air valve 6 provided with a level gage, a valve element 3 is inserted in a valve casing 2 having an exhaust-gas port 1 formed on the top. In an air valve 4, the valve element 3 floating with liquid introduced in the valve case 2 to close the exhaust-gas port 1. The air valve 4 is provided with a level gage 5 so as to indicate a level h of the liquid introduced into in the valve casing 2. Just making visual observation of a float 16 in the level gage 5, an operator can recognize malfunction such as leakage, or blockage of the air valve 4, and the malfunction of the air valve 6 provided with a level gage can be promptly repaired.