To prevent a fixing part of a rotation transmitting member from being damaged by concentration of stress.

A fixing part 8C of the rotation transmitting member 8 is fixed to a nut member 14 of a damper mechanism by a bolt 10. The bolt 10 is integrally provided with a head part 10A, a screw part 14B screwed into the nut member 14, and a flange 10C. The flange 10C has a seat diameter D3 larger than an outside diameter D2 of the head part 10A and a seat diameter D1 of the nut member 14, and a distance (d) between a peak generation region P1 of compressive stress in the fixing part 8C and a peak generation region P2 of tensile stress in the fixing part 8C is separated, and the stress is prevented to concentrate in one portion.