To hold a valve in an opening position so as to be capable of being released.

A pressure of air from the outside 2, against a spring 24, forcedly opens an elastic film 28 of a valve, so as to make air advance in the inside. In lock mechanisms 30, 30', 32, a lock is twisted to be engaged, to be held in an opening position, also when the lock is further twisted, or twisted in an opposite direction, the lock is disengaged, by the spring 24, stroke and an air pressure in the inside, the valve is closed. Further, the valve can be opened by pressing it from the outside at an arbitrary time, thereby a pressure in the inside 4 can be adjusted.