PURPOSE: To cause an air chamber to be operated as a pressure accumulation device, accommodate for a pulsation of compressed air with an air chamber and make a stable state of compressed air supplied from the air chamber to a fuel injection valve by a method wherein the air chamber is disposed in a compressed air passage-extending from an air pump to the fuel injection valve.

CONSTITUTION: A fuel injection device 46 for injecting and supplying fuel to a combustion chamber 37 has a high pressure fuel injection valve of a solenoid opening or closing type. A fuel pump 56 for use in feeding compressed fuel to an injection valve 48 is driven by an engine 16 through a power transmission device 17. In addition, an air pump 67 for use in supplying compressed air to a high pressure fuel injection valve 48 and a differential pressure regulator 62 is also driven by the engine 16 through the power transmission device 17. In this case, a discharging port of the air pump 67 is connected to the high pressure fuel injection valve 48 with the first pressurizing pipe 69 acting as a compressed air passage. Then, an air chamber 71 is disposed in the midway part of the first pressurizing pipe 69.