PURPOSE: To cause no lack of fuel during lower loading of an engine, by straightghtening the downstream negative suction pressure in suction passage of an engine with a straightening circuit to cause a relatively low negativel pressure, and by applying the negative pressure the vicinity of an injection outlet at the tip of a fuel supply passage.

CONSTITUTION: A branched path 8 is so formed that it is positioned near the injection outlet 5 of a fuel supply passage 6 and is extended in the downstream side of a suction passage 2 through a straightening circuit 11 consisting of a check valve 9 and an orifice 10. And the downstream suction negative pressure of said passage 2 is made rather lower and applied the vicinity of said injection outlet 5. Thus, since the fuel sucked through said passage 6 is increased, lack of the fuel can not be caused during lower loading of an engine.