An optical scanning device that uses a light spot to scan an image surface with a light source, a deflector, and an imaging element includes a housing in which the light source, the deflector, and the imaging element are set. The housing includes at least two sidewalls opposed to each other, a bottom surface that extends substantially perpendicular to the sidewalls, and ribs that are substantially perpendicular to the bottom surface and formed to extend from the two sidewalls, respectively. Discontinuous sections (sections between ribs or notched sections of the ribs) for passing light beams are provided in the ribs. A reinforcing member separate from the ribs are bridged to the discontinuous sections.