PURPOSE: To perform accurate fuel injection all the time, by spraying a jet of liquefied gas in a liquid state, while regulating its returning fuel pressure with suction pipe pressure and fuel pressure in combination.

CONSTITUTION: Liquefied gas fuel inside a tank 25 is fed with pressure to a pump 21 as being kept in a liquid intact and sprayed out of an injection valve 27 into a suction pipe. Superfluous fuel out of this injection valve 27 is regulated in pressure by a valve 37 and returned to the tank 25 via a pipe 24. The valve 37 is operated by diaphragms 30 and 29 which operate so as to open the valve 37 when pressure in the suction pipe 26 is low and lowers injection pressure in the injection valve 27, making it balance with suction pipe internal pressure. And, when the fuel pressure in the tank 25 becomes high, this pressure acts on the diaphragm 29 and operates so as to open the valve 37.