PURPOSE: To perform simple and high-precise control of a fuel injection amount, by a method wherein, based on the number of revolutions of an engine and a step-in amount of an accelerator pedal, a reciprocating drive means is electrically controlled, and spill ring coupled to a pump plunger is driven.

CONSTITUTION: A spill ring 16 is slidably engaged with a pump plunger 8 disposed in a pump chamber R of a pump casing 1. A rack 18 is secured on the outer peripheral surface of the spill ring 16, and a pinion 20 secured on a shaft 19 is engaged with the rack 18. In this case, the one end of the shaft 19 is coupled to a forward and reverse rotatable stepping motor 22 through a reduction gear mechanism 21 mounted on the outer peripheral surface of the pump casing 1. The stepping motor 22 is controlled by a control computer C by means of detecting signals from a number of revolutions detector 23 and an accelerator pedal step-in amount detector 24 as well as a rotary encoder 22a incorporated in the stepping motor.