An optical scanning device includes a light source that emits first and second light beams, and an optical splitter to which the first and second light beams deflected by an optical deflector are incident. Principal rays of the first and second light beams incident to the optical splitter are nonparallel to each other in a plane orthogonal to a main-scanning direction. Transmitted light from the optical splitter out of the first light beam and reflected light from the optical splitter out of the second light beam are guided to corresponding scanning target surfaces, and transmitted light from the optical splitter out of the second light beam and reflected light from the optical splitter out of the first light beam reach none of the scanning target surfaces.