An optical scanning device includes plural light source devices, a deflecting device having deflecting surfaces, an input optical system and a plurality of imaging optical systems, wherein a plurality of scan surfaces are simultaneously scanned by the deflecting device, wherein each of the plurality of imaging optical systems includes at least one transmission type imaging optical element and at least one reflection optical element, wherein each of at least two light beams scanningly deflected by the different deflecting surfaces of the deflecting device passes through the at least one transmission type imaging optical element constituting the imaging optical system and is thereafter reflected by the at least one reflection optical element and, subsequently, it passes again through the transmission type imaging optical element, and wherein, after passing again through the transmission type imaging optical element, the at least two light beams scanningly deflected by the different deflection surfaces of the deflecting means intersect with each other within a sub-scan section.