Abstract: An optical scanner can inhibit the quantity of thermal deformation and the variation of an optical path of an optical box attached to the frame of an image information device. In the scanner, a fixed part fixed to the frame of an image formation device is provided in a part of which the rigidity is relatively low apart from the corner in the vicinity of the vertex of the outside shape of the bottom of which the rigidity is relatively high in an optical box. Hereby, deformation of each part (in the vicinity of the corner and the side) by stress caused in the optical box due to a difference in the coefficient of linear expansion between the frame and the optical box as temperature in the image formation device varies can be uniformed, and warp like adrum that is apart to which an optical component is attached, that is, the bottom is tilted, which is the worst mode of deformation out of the variation of an optical path, can be reduced.