| 摘要 |
PROBLEM TO BE SOLVED: To perfectly hermetically seal a gap at the base part of an image- formation lens. SOLUTION: The image-formation lens 4b forms scanning light by a rotary polygon mirror into an image on a photoreceptor, and is positioned in an optical axis direction by making both ends of the lens 4b abut on the X reference surface 12a of a reference shape part 12 erectly provided on an optical box 10. A groove 10c in which an elastic member 13 for hermetically sealing the gap at the base part of the lens 4b is inserted is formed on the base wall of the optical box 10. By bringing both end faces of the member 13 into contact with the end face of the groove 10c and the side surface 12b of a reference shape part 12, the air infiltrating to the rotary polygon mirror side from the periphery of the lens 4b is intercepted. |
