Abstract: A device for preventing an overrunning operation of an internal combustion engine, provided in a capacitor discharge type ignition system comprising a magneto generator including an ignition power coil and at least one loading coil and an ignition circuit including a capacitor arranged to be charged from said ignition power coil of said magneto generator, an ignition coil and a discharging thyristor so arranged that energy from said capacitor is discharged through the primary side of said ignition coil when said discharging thyristor is triggered in time with said internal combustion engine, said device comprising an ignition failing thyristor provided so as to shunt said discharging thyristor whereby a discharge current from said capacitor is prevented from flowing through said ignition coil and also means to prevent a hysteresis on repetition of failure and success to ignite said engine. The ignition failing thyristor is adapted to be triggered by a voltage responsive to the revolution number of the engine.