To provide a mechanism for preventing looseness of a screw that prevents the screw from loosening without using adhesive.

A cam 14, in which a square rod part 12 of a rotary shaft 11 is fitted to a hole 14a, and a washer 17 with a claw, in which a projection 16 of the cam 14 is engaged with an engaging hole 18b, are fixed to the rotary shaft 11 using a bolt 19. In addition, the claw of the washer 17 with the claw is bent and raised in a direction of a head of the bolt 19 to abut against a flat part on a side in an axial direction of the head of the bolt 19.