Gas fuel supply apparatus

An engine-start is inhibited when a gas engine is tilted, and the engine is immediately stopped. A shutoff valve is provided on a liquefied fuel passage supplying a liquefied fuel to a vaporizing chamber from a cylinder. The shutoff valve is provided with a diaphragm to which a pulsation pressure of a crank chamber is applied, and opens the liquefied fuel passage if a negative pressure is applied to the diaphragm. A tilting shutoff valve is provided in a pressure passage transmitting the pulsation pressure to the shutoff valve. The tilting shutoff valve which has a ball valve releases the pulsation pressure of the crank chamber to an atmospheric air. If the pulsation pressure is open to the atmospheric air, the diaphragm can not operate. Accordingly, the liquefied fuel passage is kept being shut off, and is rapidly shut off in response to the tilt during the operation.