Patent ID: 7441553

Claim:
An ignition coil adapted to being mounted to a sparkplug, the ignition coil comprising: a coil body including a primary coil and a secondary coil; and a plug cap provided to an axial end of the coil body, wherein the coil body is adapted to being mounted to the sparkplug via the plug cap, the plug cap has a plug-fitting hole adapted to being axially fitted to an insulator of the sparkplug, the plug cap has an end surface defining the plug-fitting hole, the end surface includes circumferential portions respectively located at axial positions each being variously changed with respect to a circumferential direction, and the circumferential portions and inner circumferential edges of the end surface are configured to be in continuous contact with an outer circumferential periphery of the insulator of the sparkplug about an entire circumference of the insulator, whereby the plug cap and the insulator are electrically insulated and sealed with respect to one another to define a water-proof structure.