A laser scanning device includes a polygon mirror, one or more lenses, and a plurality of light shielding plates. The polygon mirror reflects a light beam during rotation of the polygon mirror. The lenses allow the light beam reflected off the polygon mirror to pass through the lenses. The plurality of light shielding plates are arranged at a distance from each other and block an undesirable beam, which is part of the light beam, reflected off at least one of the lenses and heading for an optical device. The plurality of light shielding plates form an air channel that allows an air current generated by the rotation of the polygon mirror to flow through the air channel.