To provide a rotary support mechanism, keeping the relative angular displacement of two member rotatably coupled to each other without a hook, securing the relative angular displacement of two members 180° or more, and having excellent durability.

Although first to third projecting parts 71, 73, 75 of a driving cam 33 are received by first to third recessed parts 51, 53, 55 of a fixed cam 31 to be positioned when the relative angle between the driving cam 33 and the fixed cam 31 is a reference angle, they are abutted on a first reference surface 65 of the fixed cam extending over 180°or more when the relative angle is any angle other than that. In that case, a rotating shaft 19 is included in the inside of a polygon M obtained by connecting three or more points belonging to the abutting part. Accordingly, the fixed cam 31 and the driving cam 33 can be prevented from being tilted by energizing force of a disc spring during the relative rotation. Thus, it is possible to decrease uneven abrasion of the fixed cam 31 and the driving cam 33 and abrasion of a shaft supporting the cams.