To simplify an elastic pressurizing mechanism with which a rotating polygon mirror is assembled on a rotor of the driven part of the rotating polygon mirror.

The rotor 5 which rotationally drives the rotating polygon mirror 1 is built in a unit with a supporting member 4 fixed to a rotating shaft 3, the rotating polygon mirror 1 is mounted on the supporting member 4 and made in a unit with the rotor 5 or the like by being pressurized by an elastic member 8. The elastic member 8 has a push-nut formed part 8a inside of an abutting part 8b which is abutted to the rotating polygon mirror 1, and the elastic member 8 is directly fixed to the rotating shaft 3 by making the push-nut formed part 8a break into the surface of the rotating shaft 3.