PURPOSE: To save a space for mounting by integrally forming a large diameter valve and a small diameter valve inside a casing and providing them with variable orifice function.

CONSTITUTION: A pneumatic valve possesses a construction wherein a small diameter valve 1 is enclosed inside a large diameter valve 3 which reciprocates inside a casing 4. Both valves are set in a closed state at first, then the small diameter valve 1 becomes open by ejecting valve driving high pressure air 8 from an air port 7 for opening, and a small quantity of gas flows from the IN port of the pneumatic valve to the OUT port. Next, the large diameter valve 3 becomes open by switching the valve driving high pressure air 8 from an air port 6 for closing to an air port 5 for opening, and a large quantity of gas flows from the IN port to the OUT port of the pneumatic valve.