FASTENING STRUCTURE

A fastening structure includes an insulation member disposed between a fastening member and a fastened member, and has a configuration wherein the insulation member is in close contact with the fastening member and the fastened member so that an adequate sealing area is secured. The fastening structure includes: a case; a fastening member extending through a through hole in the case; and an insulation member between the fastening member and the case. The fastening member includes a portion exposed from the case, and a penetrating portion extending through the through hole. The expose portion includes a confronting surface opposed to an outside surface of the case via the insulation member. A compression region is located, and defines a minimum distance between, the confronting surface and the outside surface. A projection is disposed at place not overlapping with the compression region.