PURPOSE: To prevent the defective function of a nozzle being due to rust and to carry out effective fuel injection by checking the remaining of water emulsion fuel in the injection nozzle holder of a water emulsion fuel injection device of a diesel engine to restrain the occurrence of rust resulting from the moisture of the water emulsion fuel.

CONSTITUTION: The introducing oil pathes 27-30 for duel oil used for a diesel engine are provided in a pressure spring chamber inside the injection nozzle holder of the water emulsion fuel injection device of the diesel engine, and the fuel oil is returned from a leak-off screw part 49. As another example of execution, both oil passages for introducing and discharging the fuel oil used for the diesel engine into the pressure spring chamber in the nozzle holder are provided in the lead-off screw part.