A tubular trembler supported on an ultrasonic vibrator is disposed almost on an axis in an engine intake pipe and has a fuel passing-through hole in the wall thereof. A fuel jet tip of the electromagnetic injection valve is disposed so as to face the fuel passing-through hole so as to jet the fuel divergently against an inside wall of the tubular trembler through the fuel passing-through hole. The fuel is injected against the inside wall of the trembler through the fuel passing-through hole and is atomized. When the fuel is jetted into the fuel passing-through hole from the fuel jet tip, the relative distance from the fuel jet tip to the inside edge of the fuel passing-through hole is determined so that most of the injected fuel will strike the inner wall of the tubular trembler, within the dimensions determined by the bore, the fuel passing-through hole, the inside diameter and the length of the tubular trembler and the angle of the spread of the injected fuel.