A leaf spring configured to mount an optical element to a housing, the housing containing: a rotary polygon mirror configured to deflect a laser beam emitted from a light source; and the optical element configured to guide the laser beam deflected by the rotary polygon mirror to a member to be scanned, wherein an adhesive is applied to the leaf spring, the adhesive being configured to adhere separated material scraped from the housing, the separated material being scraped from the housing by rubbing between the leaf spring and the housing at a time of mounting the optical element to the housing.