PURPOSE: To improve the acclerating performance of a diesel engine, by increasing fuel supply in response to the output signal produced when the depth of depression on the accelerating pedal has exceeded a preset reference value.

CONSTITUTION: Output voltage of a potentiometer 1 attached to a control lever of a fuel injection pump coaxially therewith is proportional to the depth of depression of the acclerator pedal and the voltage is applied directly to the non- inverted side of a differential amplifier 2. Further, the voltage produced by passing the output voltage of the potentiometer 1 through a delay circuit consisting of a resistance R and a capacitor C is applied to the inverted side of the differential amplifier 2, and the differential voltage is compared with a preset reference value at a comparator 3. With such an arrangement, when the output of the differential amplifier 2 becomes higher than the reference value, a transistor 4 is turned ON and a solenoid valve 5 is opened to introduce negative pressure from a vacuum pump 6 into a vacuum chamber 71 of a vacuum actuator 7. Resultantly, a rod 8 of the vacuum actuator 7 is moved to the left in the drawing, so that fuel supply is increased.