An optical scanning device includes plural sets of optical paths, and in each set of optical paths, first and second light beams emitted from the two light sources having an opening angle in the main scanning direction are orthogonal to a deflection axis of a deflector and are deflected and scanned by the same surface of the deflector at different positions deviating from each other in a deflection axis direction. A first imaging optical element gives positive optical power to the deflected light beams to converge the light beams. A focal position exists between the first imaging optical element and a second imaging optical element arranged on the optical paths in front of first and second surfaces to be scanned on two photoconductive drums. A separation distance exists between the light beams.