PURPOSE: To improve engine restarting performance and prevent the car knocking and engine stall by shielding the intermediate part to an injector chamber when an engine is in stop by a diaphragm mechanism which is moved in correspondence with the negative pressure in an intake pipe, while by opening the part when the engine is in operation.

CONSTITUTION: When the temperature in a bonnet rises, the fuel in a float chamber 4 and a cylinder chamber 5 pushes up an outlet valve 6, and passes through an injector chamber 7 and jets out from an injector nozzle 8. Since the intermediate part to the injector chamber 7 is shielded by a diaphragm spring 12, injection is prevented. Accordingly, fuel does not jet out from the nozzle 8, and a spark plug in the cylinder is not wetted, and the restart performance is improved. Further, the injection chamber 7 is filled with fuel. When the engine is started, a negative pressure is generated on the downstream side of a throttle valve 1, and the negative pressure acts on a diaphragm 10 from a negative pressure passage 13, and the diaphragm 10 is lifted up, overwhelming the spring 12, and the injection chamber 7 is opened, and communicates to the nozzle 8, and fuel is discharged with high response.