An optical scanning device includes a light source having a plurality of light-emitting portions, a deflector for deflecting a plurality of light beams emitted by the light source, optical elements for guiding the plurality of light beams emitted by the light source toward the deflector and an imaging element for guiding the plurality of light beams deflected by the deflector onto a surface to be scanned. A polarization limiting element is inserted in an optical path between the light source and the deflector so as to limit directions of polarization of the plurality of light beams.