PURPOSE: To protect an ignition coil and a transistor by giving the output of an AND gate which obtains the logical product of a rotation pulse output and the output of a rectification and time constant circuit, to the base of a transistor.

CONSTITUTION: A pulse output which is generated at an interrupter by means of the rotation of an engine, is given to the base of a transistor 8, which is turned on and off to generate a high voltage on the secondary side of an ignition coil 7, causing an ignition plug to be ignited through a distributor 8. In this case, a rectification and time constant circuit 9 which rectifies the pulse output, and an AND gate 10 are provided, and the logical product of the pulse output and the output of the circuit 9 is obtained by the AND gate 10, whose gate output is given to the base of the transistor 6. Accordingly, even when the engine is stopped during a warming-up operation and, further, the contact point of the interrupter is closed while the engine is stopped, the output of the rectification and time constant circuit 9 becomes L after the time constant of a capacitor 92, thereby, turning off and protecting the transistor 6.