PURPOSE: To obtain an ignition system having a long duration time of ignition, by generating a driving signal on the basis of an AC output signal by an oscillator so that high voltage is generated and applied to an ignition plug when said driving signal and a timing control signal are simultaneously received.

CONSTITUTION: Photointerrupters 4aW4d correspndingly provided to each cylinder are successively turned on by rotating a disc shaped shutter, in a part of which a notch is provided, and an output signal of those photointerrupters is input to a processor circuit 10. In the processor circuit 10, the input signal, after being amplified, is applied to the base of a transistor Q1a, causing the transistor Q1a to be turned on also a transistor Q2a to be simultaneously turned on, and battery voltage is fed to the center tap of a primary winding of an ignition transformer T (T1WT4). While at this time, high voltage is induced in a secondary winding of the ignition transformer T, which alternately connects signal lines Y, Z to the earth in accordance with the output signal frequency of an operation amplifier IC1 functioning as an oscillator, and said high voltage is applied to ignition plugs SP1WSP4.