PURPOSE: To efficiently provide a signal source, by a method wherein a capacitor for signal source is charged through a transistor by means of a halfwave output from a capacitor charging coil, and when a charging charge is increased to higher than a set value, the transistor is disconnected.

CONSTITUTION: A title ignition device charges an auxiliary capacitor 3 by means of the one halfwave output from a capacitor charging coil 1, and charges a capacitor 15 for ignition by means of the other halfwave output. By means of an ignition signal from an ignition control circuit 13, a thyristor 16 for ignition is energized to discharge the charge of the capacitor 15 for ignition to the primary side of an ignition coil 18. In which case, a series circuit of a transistor 6, a diode 11, and a capacitor 12 for signal source is connected in parallel to the auxiliary capacitor 3. When the terminal voltage of the capacitor 12 for signal source is increased to a give value, the transistor 6 is disconencted with the aid of shut-off control circuits 7W10, the charging charge of the capacitor 12 produces the power source of the ignition control circuit 13.