An optical scanning device includes a rotating polygon mirror, a light source that irradiates first and second light beams at one side of the rotating polygon mirror and irradiates third and fourth light beams at the other side thereof, a first optical element that reflects the first light beam and allows the second light beam to pass therethrough, a second optical element that reflects the second light beam, a third optical element that allows the third and fourth light beams to pass therethrough, and a fourth optical element that reflects the fourth light beam. The second light beam is a light beam corresponding to yellow, the first, the third, and the fourth light beams are light beams corresponding to three colors other than the yellow. Between the third and fourth optical elements, a scanning lens is arranged. Between the first and second optical elements, a scanning lens is not arranged.