A multi-beam scanning device is provided with a light source that emits a plurality of light beams, a polygonal mirror that deflects the light beams to scan, and an optical system that converges the deflected light beams on a plurality of objects to be scanned. The objects are arranged on a side, with respect to the polygonal mirror, in which the light beams scan, from a position closer to the polygonal mirror to a position farther from the polygonal mirror in order. The optical system further includes a plurality of optical path turning systems that turn optical paths of the deflected light beams, respectively. Each of the optical path turning systems includes a plurality of reflection surfaces, the numbers of the reflection surfaces of the optical path turning systems are all even, or odd.