PURPOSE: To eliminate countermeasure against breaking of wire such as increasing of the number of turns, by charging an ignition capacitor with high voltage being induced when a semiconductor switching element for shortcircuit is interrupted thereby decreasing the diameter of wire of a coil for charging the capacitor.

CONSTITUTION: An A.C. voltage waveform is produced in a capacitor charging coil 3 through rotation of a crankshaft. When a halfwave output is produced in the charging coil 3 in the direction of a solid line arrow (negative direction), a circuit power source capacitor 11 is charged. When a halfwave output is produced in the charging coil 3 in the direction of a dot line arrow (positive direction), said positive halfwave output is shortcircuited by a current, interruption transistor 16. When the halfwave output increases, the current interruption transistor 16 is interrupted so as to interrupt the shortcircuit current abruptly. At this time, a large induction voltage is produced in the coil 3 and an ignition capacitor 23 is charged with said high voltage. Since the inductance of the coil 3 can be increased, the wire diameter thereof can be reduced thus eliminating the necessity for increasing the number of turns.