PURPOSE: To eliminate need of an auxiliary air pump by providing an auxiliary air supply means using exhaust pulsation for a drive source in the middle of an auxiliary air passage for a type having the auxiliary air pass-age to take auxiliary air from a suction passage on the upstream of a suction throttle valve and supply it to a fuel injection valve.

CONSTITUTION: A fuel injection valve 30 is provided at a close position to a suction port 16 to be directed to a combustion chamber 4 in a suction passage 10 on the downstream of a suction throttle valve 26 of an internal combustion engine 2, one end side is connected with the suction passage 10 on the upstream of the suction throttle valve 26, and the other end side is provided with an auxiliary air tube 32 connected with a fuel injection valve 30. Auxiliary air taken from the suction passage 10 is supplied to the fuel injection valve 30, so formation of fine grains of injected fuel is accelerated. In such a fuel injection device 28, an auxiliary air supply means 36 having a diaphragm 40 driven by exhaust pulsation generated in an exhaust passage 14 for supplying the auxiliary air taken from the suction passage 10 is provided.