Abstract: An inner fixed shaft of a scanner motor is secured to a housing by a screw. A rotary polygon mirror is attached to the inner fixed shaft through bearings of a cylindrical portion. A spiral-shaped rib or groove is formed on the housing at least on the lower side of the rotary polygon mirror. When the rotary polygon mirror is rotated, an air current is generated in accordance with the rotation of the rotary polygon mirror. This current becomes an air current flowing toward a base portion of the inner fixed shaft of the scanner motor to prevent an oil component dispersed or volatilized from the bearing portion from being moved toward the rotary polygon mirror and the direction of optical devices disposed around the rotary polygon mirror. Moreover, it is possible to alleviate a wind noise generated from the rotary polygon mirror.