half wave d c current is thus smoothed out a voltage induced in the capacitor c 4 is applied to the key switch detecting section 6 the rotation detecting section 7 and the timer section 10 a discharge current from the capacitor c 4 flows to ground via the resistor r 5 and transistor tr 1 already turned on and also via the resistor r 13 and transistor tr 5 therefore the transistor tr 2 of the rotation detecting section 7 is kept off along with the transistor tr 3 of the actuator drive section 8 when the engine 31 is normally driven in fig3 the control rack 14a of the fuel injection pump 14 is operated by balance of the governer weight not shown and the governer spring 20 to constantly control an engine speed next the contact point 1a of the key switch 1 in fig2 is shifted to the on terminal to the off terminal so as to stop the engine 31 the base current of the transistor tr 1 is cut off so that the transistor tr 1 is turned off to produce an engine stop signal also the charge current to the capacitor c 2 is cut off after that the transistor tr 5 is kept on until a period of time corresponding to the time constant tset determined by the resistance of the resistor r 11 and the capacitance of the capacitor c 2 elapses when the transistor tr 1 is turned off a discharge current from the capacitor c 4 flows to the transistor tr 5 while turned on via the resistor r 13 the discharge current further flows to the resistor r 6 via the resistor r 5 so.