An optical scanning device includes a polygon scanner that deflects and scans light beams, a body on which the polygon scanner directly mounted, and a heat dissipating unit that dissipates heat of the deflection scanning unit. The heat dissipating unit is located at a position on an outer surface of the body corresponding to the deflection scanning unit. The body is provided with a pair of wall portions on the outer surface. The wall portions face each other with the heat dissipating unit between them, and extend in a direction in which air blown by an air blowing unit flows to form an air-flow path.