IGNITION SYSTEM

An ignition system that uses a technique capable of restraining radiation of noise caused by discharge of a spark plug in the ignition system. The ignition system includes a spark plug (10) and a power supply section. The spark plug (10) is attached to an engine head (20). The power supply section has a battery having a ground terminal, and an ignition coil which transforms a voltage of the battery and supplies a transformed voltage to the spark plug. In the ignition system, a metallic shell (130) of the spark plug (10) is fixed to the engine head (20) while being electrically insulated from the engine head through an insulator (22); an electrically conductive path (40) is connected to the metallic shell (130); and the electrically conductive path (40) is electrically connected to the ground terminal of the battery while being electrically insulated from the engine head (20).