PURPOSE: To improve the ignition performance of low grade fuel by atomizing fuel which is jetted from a injection valve, by an air flow atomizing means so as to allow the atomized fuel to be blown further into the inner surface of an ultrasonic vibration atomizing device for further atomization.

CONSTITUTION: Air is inducted into an air intake pipe 13 at the upstream of a throttle valve 9 in a suction pipe 4 so as to allow the air to be jetted around a nozzle 17 of an injection valve 12. A cylinder 10, which has a hole 18 in front of the nozzle 17, is provided. In addition, an ultrasonic atomizing device 11 is provided to the cylinder 10. In this configuration, fuel, which is atomized by air flow around the nozzle 17, is jetted into the cylinder 10 where small particles are conveyed downward by the air flow from the upper side, and large particles are atomized while they are subjected to ultrasonic vibration after they have hit against the inner wall of the cylinder 10. The device allows the average diameter of fuel particles to be made small so as to improve the ignition performance of low grade fuel.