An optical scanning device includes a plurality of light sources, a light deflector, and a single scan lens. The light deflector deflects a plurality of light beams emitted from the light sources by a same face for scanning a plurality of to-be-scanned portions simultaneously. The single scan lens receives the light beams from the light deflector and focuses the light beams onto each of the plurality of to-be-scanned portions to scan the to-be-scanned portions simultaneously. The single scan lens is used in common for the light beams, and has one incidence plane and a plurality of exit planes in a sub-scanning direction separately prepared in the sub-scanning direction for each of the to-be-scanned portions. The incidence plane has a refractive power of the lens in the sub-scanning direction decreasing toward peripheral portions in the main scanning direction. The exit planes have positive refractive power in the main and sub-scanning directions.