PURPOSE: To improve operation performance in each operational region, by using only a premixing route in the time of start and idle operation, two systems of premixing route and direct injecting route in the time of low load operation and only a direct injection system in the time of high load operation, in the case of a supply system of hydrogen gas.

CONSTITUTION: Hydrogen gas in a fuel tank 2 passes through a pressure reducer 3 being supplied to an engine 1 from two systems of a direct injection route 4, directly injecting the gas to the engine 1, and a premixing route 5 sucking the gas from an intake control valve 6 through an intake manifold 7 together with suction air. The engine 1 provides a mechanical flow control valve 11 directly connected to an accelerator 10, electronic proportional control valve 12 and a shutoff valve 13 in the direct injection route 4 while an injector system 15, regulating system 16, main system 17 and an amount increasing system 18 in the premixing route 5. A control unit 25 performs switching being based on various parameters so as to use only the premixing route in the time of start and idle operation, two systems in the time of low load operation and only the direct injection system in the time of high load operation.