Abstract: Two ignition plugs are provided for each cylinder of an engine. Since it is desirable that these two plugs be sparked by one ignition coil, separate output terminal of a secondary coil of the ignition coil are respectively connected to each of the two plugs. An impedance circuit element is provided between one terminal of the secondary coil and ground to disturb a balance of the output voltages from the secondary coil terminals. The voltage of the other terminal of the secondary coil then reaches the break-down voltage between the air gap of its respective ignition plug first due to this imbalance of terminal voltages. The voltage of the one terminal then reaches the break-down voltage between the air gap of its respective ignition plug after the breaking-down of the other ignition plug. The two ignition plugs of each cylinder can thus be sparked at approximately the same time by providing the impedance circuit element between one output terminal of the ignition coil and ground.