To solve a problem wherein injection start delay time Tds from turning on of a solenoid valve to start of injection is varied and injection accuracy is deteriorated when a seat diameter Dns of a needle end is varied by aging effect.

A control chamber outlet 51 of a delivery passage 32 is opened on a side near a command piston 35, and thereby a pressure is started to be lowered in a control chamber 33 from the side near the command piston 35 when the solenoid valve is turned on and the delivery passage 32 is opened. A piston receiving pressure Pcc is rapidly lowered, and thereby variation of the injection start delay time Tds can be restrained, and variation of an injection amount and injection timing can be restrained even when there is dispersion in the seat diameter Dns and an opening valve pressure Popn is varied. The pressure is rapidly raised on the side near the command piston 35 when a valve of the injector 3 is closed, and a lowering speed of a needle 36 can be quickened, sharpness of injection end can be enhanced, and deterioration of exhaust can be restrained.