PURPOSE: To eliminate the necessity for a stop button in an engine and improve its controllability, by shorting the primary side of an ignition coil with a negative pressure switch, operated by negative pressure in an intake pipe, and stopping the engine.

CONSTITUTION: When a fuel cock 4 is swivelled to a lateral position, a communication hole 14 is not aligned to a hole 15 then fuel is shut off by a shaft 13 and stopped flowing. While a communication hole 22 is aligned to a connection pipe 24 and hole 25 to obtain their communication, then negative pressure in an intake pipe is acted upon a negative pressure chamber 28 in a negative pressure switch 7 causing the flexion of a diaphragm 27 to turn on the negative pressure switch 7, thus the primary side of an ignition coil 33 is shorted to automatically stop an engine. Then the negative pressure in the intake pipe is produced also for a short time of continuous running operation by inertia of the engine, and this negative pressure causes the negative pressure switch 7 to maintain a state of short-circuit for the ignition coil 33 till the engine is surely stopped.