An optical scanning device includes two scanning units which are disposed opposed to each other with a scanning deflector arranged therebetween, wherein one scanning unit has first and second imaging optical elements while the other scanning unit has third and fourth imaging optical elements, wherein the one scanning unit includes a light blocking member for intercepting unwanted light reflected at an optical surface of the fourth imaging optical element, wherein the third imaging optical element is provided at a light path between the fourth imaging optical element and the first light blocking member, and wherein the third imaging optical element has a positive refracting power in the sub-scan section through which unwanted light reflected at the optical surface of the fourth imaging optical element passes.