PURPOSE: To shorten the risetime and falltime of fuel injection by a method wherein the displacement of a needle at a fuel injection nozzle of a Diesel engine is controlled by controlling the pressure supplied to a needle holder, and the control of the pressure is effected by two flow-controllable valves.

CONSTITUTION: Compressed fuel is supplied from a fuel compressor 10 to an oil sump 21 at the fuel injection nozzle 17 and is fully charged. In this condition, a control valve 37 is throttled, while a control valve 38 is fully opened. As a result, the pressure in a chamber 29 of the needle holder 25 is rapidly lowered below the pressure of the sump 21, the needle 19 is moved upward, a nozzle hole 20 is opened and the fuel is injected. When the valves 37 and 38 are switched over to the fully opened position and the fully closed position, respectively, the pressure in the chamber 29 is rapidly increased so that the needle 19 is lowered to plug up the needle hole 20. Accordingly, the pressure change characteristics of the chamber 29 is improved, the resetime and falltime of fuel injection are shortened and the device becomes able to response to a change in 1ms or below.