Abstract: This device is to be installed between the origin of a gas supply and a gas supply pipe on a gas utilizing tool. As a diaphragm moves up, due to the difference in atmospheric pressure inside a chamber of the device, a first magnet positioned on an elastic plate is moved up by the magnetic forces of mutual attraction from second magnets secured to a plate on the diaphragm. The first magnet is subject to moving out of the magnetic attraction force area by the repulsion of the magnets and the force of restitution of the elastic plate. The supply of gas is dependent on the opening of a valve mounted on the elastic plate. As the first magnet moves away from the plate on the diaphragm, the magnetic forces of the first magnet move a lead-switch to the "ON" state to indicate gas is flowing.