Patent ID: 7646277

Claim:
An ignition coil inserted in a plug hole of an engine, the ignition coil comprising: a coil part including a primary coil, a secondary coil, a soft magnetic center core, and a soft magnetic peripheral core, wherein: the primary coil and the secondary coil are disposed in layers generally coaxially with each other; the center core is disposed on an inner circumferential side of the primary coil and the secondary coil; and the peripheral core is disposed on an outer circumferential side of the primary coil and the secondary coil; a connector case part made of resin and having a connector area, to which an electric wiring is connected, wherein: the coil part is inserted in the plug hole of the engine, and the connector case part is disposed outside the plug hole; an axial end portion of the peripheral core of the coil part is inserted in an insertion hole of the connector case part; and the peripheral core and an inner wall surface of the insertion hole define a ventilation clearance therebetween; an annular seal rubber attached to an outer circumference of the connector case part, wherein: a gap between the connector case part and the plug hole is sealed with the seal rubber; and the seal rubber is closely-attached to the plug hole and the connector case part along a whole circumference of the seal rubber around a central axis of the coil part; and a ventilation passage including the ventilation clearance and a ventilation hole that is formed at a certain position of the connector case part away from the seal rubber to communicate with the ventilation clearance and to communicate with an outside of the connector case part, wherein the plug hole is ventilated to the outside of the connector case part through the ventilation passage.