An optical scanning device includes: a light source; a polygon scanner that deflects a light beam output from the light source; and various types of optical elements for focusing the light beam deflected by the polygon scanner onto a desired position on a surface to be scanned, wherein a hole or a thin-walled portion that is provided on an arrangement surface of an optical housing on which the polygon scanner and an optical element having power in a sub-scanning direction are arranged, wherein the hole or a thin-walled portion extends along a main-scanning direction, and is provided near to the optical element having power in the sub-scanning direction between the polygon scanner and the optical element having power in the sub-scanning direction.