To provide an air valve for a tire of a bicycle or the like capable of preventing air leakage with simple structure.

This air valve A is structured by slidably guiding a piston-like movable valve 10 into a constriction 4 at a lower end of a cylindrical valve cylinder 2. Filling pressure applied through an air filling hole 6 at the upper end of the valve cylinder 2 slides the movable valve 10 downward to release a sealed state by an extending portion 15 to expose air delivery ports 13 so that a communication is provided with an air passage 1. After filling air, the movable valve 10 is returned slidingly to a predetermined position by the inner pressure of a tire 20. Then, the sealing state is achieved by the extending portion 15 so that the air passage 1 is enclosed, preventing air leakage.