To eliminate trouble causing the starting fault or operation failure of an engine by injecting an unvaporized liquefied gas along with a vaporized gas at low temperatures when injecting high pressure a liquefied gas from a fuel injecting valve by adjusting the pressure thereof to a predetermined normal pressure.

The liquefied gas in a cylinder 1 is heated by an engine cooling water in a preheating chamber 15 to vaporize it is fed into a pressure regulating chamber 18 through an entrance valve 24 to adjust its pressure to the predetermined normal pressure and fed to a fuel injection valve 5 from a communication chamber 29 through a separation chamber 28. When the liquefied gas is fed along with the vaporized gas by opening the communication passage 29 to form an opening 29C at the lower position of the separation chamber 28, the liquefied gas having high specific gravity is accumulated at the bottom part as it is, and only the liquefied gas having low specific gravity is fed from a fuel exit 30 located at a high position.