To provide an exhaust structure for an air valve, capable of always normally actuating a diaphragm by surely draining from a pressure chamber.

There is provided the pressure chamber 15a, which is in fluid communication with atmospheric air through a tiny aperture 17, formed above the diaphragm 14; and the upper end of a valve rod 19 is fastened to the diaphragm 14; while at the same time the valve body which opens or closes a large air aperture is provided in lower end of the valve rod 19 and drain hole 14e of a prescribed diameter of hole is provided on the diaphragm 14.