A pressing device includes a cam member 120, a bearing 120a, a cam portion 120b, a cam engaging portion 120c of snap fit fashion. The bearing 102a is rotatably supported by a fixation frame 115. The cam portion 120b is provided on one side of the bearing 120a and contacts a pressing lever. The cam engaging portion 120c is provided on the other side of the bearing 120a and engages with a hole 123a formed on an outer surface of a cam shaft 123. The cam engaging portion 120c engages with the hole 123a at a position away from a maximum load portion of the cam portion 120b by not less than 90 degrees phase different.