Ignition coil

An ignition coil configured to supply a high voltage to an ignition plug arranged in a plug hole having a bend, the ignition coil comprising:

• a coil main body part configured to be arranged at a proximal-side entrance part of the plug hole, the proximal-side entrance part having an inner diameter greater than that of the bend;
• and
• a joint part formed of a tubular elastic body that is bendable and deformable, the join part having a proximal end mounted to the coil main body part and a distal end to be mounted to the ignition plug,
• wherein:
• the joint part has a plurality of first ribs formed on an outer circumferential surface of a main tubular portion of the joint part, each of the first ribs extending along an axis of the joint part, the main tubular portion having a part thereof to be opposed to the bend of the plug hole;
• the first ribs are arranged continuously, on both a distal side and a proximal side of the part of the main tubular portion which is to be opposed to the bend of the plug hole, toward both a distal end and a proximal end of the main tubular portion;
• the joint part also has a plurality of second ribs formed on an outer circumferential surface of a proximal-side tubular portion of the joint part, each of the second ribs also extending along the axis of the joint part, the proximal-side tubular portion being located on a proximal side of the main tubular portion;
• and
• when viewed along the axis of the joint part, a maximum value d1 of a first rib diameter, which is represented by the diameter of an imaginary circumscribing circle having its center located on the axis and circumscribing tips of the first ribs, and a maximum value d2 of a second rib diameter, which is represented by the diameter of an imaginary circumscribing circle having its center located on the axis and circumscribing tips of the second ribs, satisfy the relationship of d2 > d1.