In the current fuel injection apparatus for an engine to be controlled either with mechanical or electronic control device, the injection method is by means of fuel pump to generate a pressure in the fuel supplying line; then, the fuel is sprayed out of a nozzle, and hit with the external air to become small particles. If a better atomization condition of the fuel is required, the only way is to increase the pressure of the fuel so as to increase the injection speed of the fuel; however, to increase the injection pressure would increase the manufacturing cost. In the current commercialized fuel injection apparatus, such as the port injection type or the throttle body injection type, the fuel-feeding pressure is ranging from 1 kg/cm.sup.2 -3 kg/cm.sup.2. In that low pressure region, the atomization condition of the fuel is far from being satisfactory; particularly in a two-stroke engine, it is rather difficult to reach a well condition under that low injection pressure because of the mixing time thereof being too short.