An ignition coil includes a primary winding, an auxiliary primary winding and an ignition high voltage generating secondary winding which are wound on the same core. The primary current from the generating coil of a magneto flows to the base of a transistor through the primary winding of the ignition coil. The primary current flowing through the primary winding induces a voltage across the auxiliary primary winding and the induced voltage is applied between the base and emitter of the transistor. At the time of ignition, the primary current flowing to the base of the transistor is shunted by a semiconductor switching element so that the transistor is turned off and the current flowing through the auxiliary primary winding is interrupted, thus generating a high voltage across the secondary winding of the ignition coil.