In a multiple gas fuel delivery system for interchangeably supplying a plurality of gas fuels having different supply pressures to an internal combustion engine, at least a pair of fuel passages extend from a gas fuel inlet (6a) to a fuel ejection nozzle (12) for delivering the gas fuel to a carburetor, and are provided with respective metering jets (13, 14). One of the fuel passages is provided with a pressure responsive valve (15) that communicates only the first metering jet (14) for delivering the fuel gas to the carburetor when a gas fuel of a relatively high pressure is used, and communicates both the first and second metering jets (13, 14) for delivering the fuel gas to the carburetor when a gas fuel of a relatively low pressure is used. Therefore, a flow switching valve is not required, and the passage structure can be simplified. Also, the pressure responsive valve (15) is actuated by the pressure of the fuel, and no manual selection is required when a different gas fuel is selected.