PURPOSE: To reduce load on a starter motor and improve servo effect by inhibiting the automatic stop of an engine before a power transmission system is connected when the engine is restarted even if negative pressure is recovered to set negative pressure.

CONSTITUTION: A negative pressure switch 23 is engaged with automatic stoppage and restart of a negative pressure detecting means, OS(One shot multivibrator)24, FF(Flip-flop)25, inverter 29 and OR gate 31 engaged with those of an automatic stoppage inhibiting and restarting means, AND gate 26 and OR gate 27 engaged with those of a inhibition releasing means and others engaged with usual automatic stoppage and restart respectively. Negative pressure is supplied from an intake manifold to a negative pressure chamber of a brake toggle joint by restarting an engine. When the negative pressure exceeds set negative pressure the negative pressure switch 23 is turned off while the output of the inverter 29 is maintained at "0". Thus, load on a starter motor is reduced to improve the servo effect of the brake toggle joint.