PURPOSE: To promptly ignite atomized fuel of a main injection so as to improve fuel consumption by performing a pilot injection prior to the main injection through a fuel injection nozzle in a combustion chamber in the top part of a piston in a diesel engine in which exhaust gas is partly returned to an intake side.

CONSTITUTION: High pressure fuel, when it is supplied to a fuel passage 33, is introduced into a chamber 40, when a free piston 37 of a reciprocating part 39 is placed in an upper position, so that a valve opening pressure is generated first low to perform pilot injection from a nozzle 34 of a nozzle main unit 36. When a pressure of fuel is increased, the free piston 37 is moved downward, till it is brought into contact with a stopper 45, to compress a spring 44 and to once close the nozzle main unit 36 because the valve opening pressure is rapidly increased, and main injection is started when a nozzle needle 35 is lifted by further increasing the pressure of fuel. The injection, when it is completed, is cut off with cutting sharpness improved by actuating a retraction valve 52. A combustion speed is improved to prevent deterioration of fuel consumption by the pilot injection of form an activated atmosphere.