PURPOSE: To increase the output of the engine by mixing the fine particles of fuel with air through two stages of injection nozzle.

CONSTITUTION: Air enters into an injector 20 from an air tank 1 through an air supplying pipe 3, an air heater 11, an air filter 12 and a pressure gauge 13. The injector 20 is provided with four sets of first stage injection nozzles 20' and one set of second stage injection nozzle 20". The fuel from a fuel supplying pipe 18 is atomized into ultrafine particles and is mixed with air at the first stage nozzle 20 and, then, the fuel is mixed with the air in the condition of ultrafine particles further in the second stage nozzle 20" perfectly. Mixture is injected into a cylinder from the injection valve through a fuel pump 21, a fuel high-pressure pipe 22 and the like.