In the related art, as an ignition system used in a combustion device of an internal combustion engine, a device, which includes a spark plug having a center electrode and a ground electrode, and forms a gap between both electrodes, a discharge power source such as an ignition coil supplying a voltage to the spark plug, and an ignition cable electrically connecting the spark plug and the discharge electrode, is known. In the above described ignition device, a high voltage is applied from the discharge power source to the spark plug via the ignition cable so that a spark discharge is generated in the gap of the spark plug. As a result, the fuel gas is ignited.
In recent years, a technique has been disclosed in which in order to improve an ignition ability, the spark discharge is generated by an AC power (a high frequency power) input from an AC power source to the gap, instead of the high voltage (for example, see JP-A-2009-8100).