PURPOSE: To improve the response performance of a solenoid valve by using a plurality of exciting coils and allowing at least one exciting coil to generate the magnetic flux in the reverse direction when electric conduction is cut-off.

CONSTITUTION: A unit injector is equipped with a pump chamber 27 which is pressurized through a plunger 23 by the revolution of a cam 26 and a fuel passage 29 which communicates to a needle chamber 30, and said passage 29 communicates to a low-pressure fuel feeding side through a control passage 40 and a solenoid valve 41. Said solenoid valve 41 is equipped with an exciting coil group 49 consisting of three exciting coils 49aW49c wound concentrically. When fuel injection is completed, an electric-current control circuit 70 deenergizes the exciting coil 49b a prescribed time before the predetermined time for fuel injection completion and energizes the exciting coil 49c having the direction of magnetic flux in the reverse direction, and the magnetic flux of the whole electric magnet is reduced speedily, and the solenoid valve 41 is speedily opened to reduce the pressure in the needle chamber 30.