To control an engine speed of an engine so as to be held at a preset engine speed without using an expensive rack position sensor for detecting a position of a control rack and without exhausting black smoke from the engine.

A signal converting means 7A is arranged for restricting a rate of change of time of an engine speed setting signal, and a deviation signal (e) is obtained by arithmetically operating a deviation between a preset engine speed and an actual engine speed from an engine speed setting signal (b) and an engine speed detecting signal (c) restricted on the rate of change of time. A manipulated variable of the control rack 2a required to zero the deviation between the engine speed setting signal (b) and the engine speed detecting signal (c) restricted on the rate of change of time is arithmetically operated by a manipulated variable arithmetically operating means 7D, and a driving signal (h) is imparted to an actuator 4 so as to displace the control rack 2a by the arithmetically operated manipulated variable.