PURPOSE: To reduce the variation rate of a revolution number of disposing a control circuit which controls the amount of fuel by means of a signal from a timer according to the estimated load variation schedule, in a control circuit controlling the amount of fuel depending on the difference between a desired revolution number and an actual revolution number of an engine.

CONSTITUTION: A control circuit (A) detects any deflection between a desired revolution number and an actual revolution number of an engine accordance to a revolution number setting device 1 by means of an adder-subtracter and after the deflection is calculated with a revolution number operation circuit 8, the amount of fuel injected from an injection pump 5 is controlled by the signal through an actuator 9. In this case, another control circuit (B) consisting of a timer 21 operated by an inputted start operation command signal and a function generator 22 is disposed additionally. A fuel control signal 15 outputted from said revolution number operation circuit 8 and a fuel control signal 25 by an estimated load outputted from said function generator 22 are inputted in an adder-subtracter 23 and a synthesized signal 26 is fed to said actuator 9, thereby controlling the amount of fuel injected from said pump 5 in such a manner that the revolution number is not deflected from the set value.