A hinge mechanism includes: a bracket 2 having a rotation shaft portion insertion hole 2a for inserting through a marginal rotating shaft portion 3b thereof, and one engaging concavo-convex section 2b; a plate 5 having a mounting shaft portion insertion hole 5a; and a leaf spring 4 having a mounting shaft portion insertion hole 4a and the other engaging concavo-convex section 4c, and located between the bracket 2 and plate 5 and mounted to the rotation shaft 3, wherein the hole 5a is formed larger than the hole 4a such that the spring 4 is caulked and fixed to the end face of the shaft portion by entering of the outer wall side part of a mounting shaft portion 3c formed on the end face of the portion 3b that is collapsed by caulking into a gap 5c formed between the portion 3c and insertion hole 5a.