A second scanning lens has a refracting power in a sub-scanning direction, and an optical element-deforming unit that changes a position of the center of curvature of the second scanning lens in the sub-scanning direction to a direction substantially parallel to the sub-scanning direction. Further, a function Cs(y) of a curvature in the sub-scanning direction of the scanning lens deformed by the optical element-deforming unit in the scanning lens is set to have only one extreme value within a mirror surface region on a first surface of the lens.