An optical scanning device deflects, by a common optical deflecting part, a plurality of groups of light beams emitted from a plurality of light sources and directs, by a scanning and imaging optical system, the groups of deflected light beams to respective scan surfaces so as to optically scan the scan surfaces. Each of the groups of light beams deflected by the optical deflecting part passes through at least two scanning lenses while being directed to a corresponding one of the scan surfaces. A first scanning lens arranged nearest to the optical deflecting part among the scanning lenses transmits the groups of light beams directed to the respective scan surfaces and satisfies Pm>0.gtoreq.Ps, where Pm is a power in a main scanning direction and Ps is a power in a sub-scanning direction. A second scanning lens arranged nearest to the corresponding scan surface among the scanning lenses possesses a positive power in the sub-scanning direction and transmits only the group of light beams directed to the corresponding scan surface.