A light scanning unit comprising: a plurality of light sources (110A- 110D) configured to emit a plurality of light beams; a deflector configured to deflect the light beams emitted from the light sources in a main scanning direction; and an imaging optical system configured to respectively focus the light beams deflected by the deflector onto a plurality of surfaces (210A- 210D) to be scanned, the imaging optical system including: a first group of reflecting members (160A, 180A) configured to change a first light path at least twice, the first light path being a path of one of the light beams directed to one of the surfaces disposed relatively far from the deflector; and a second group of reflecting members (160A, 180B) configured to change a second light path at least twice, the second light path being a path of one of the light beams directed to one of the surfaces disposed relatively close to the deflector, wherein both of a section of the second light path before a first change of the second light path and a section of the second light path after the first change of the second light path intersect a section of the first light path after a second change of the first light path, and the first and the second light paths remain on one side of the deflector from which the first and the second light paths were deflected, respectively, the light scanning unit characterized in that: the deflector deflects other light beams from another side of the deflector to create third and fourth light paths in directions opposite to the first and the second light paths, respectively. a plurality of light sources (110A- 110D) configured to emit a plurality of light beams; a deflector configured to deflect the light beams emitted from the light sources in a main scanning direction; and an imaging optical system configured to respectively focus the light beams deflected by the deflector onto a plurality of surfaces (210A- 210D) to be scanned, the imaging optical system including: a first group of reflecting members (160A, 180A) configured to change a first light path at least twice, the first light path being a path of one of the light beams directed to one of the surfaces disposed relatively far from the deflector; and a second group of reflecting members (160A, 180B) configured to change a second light path at least twice, the second light path being a path of one of the light beams directed to one of the surfaces disposed relatively close to the deflector, a first group of reflecting members (160A, 180A) configured to change a first light path at least twice, the first light path being a path of one of the light beams directed to one of the surfaces disposed relatively far from the deflector; and a second group of reflecting members (160A, 180B) configured to change a second light path at least twice, the second light path being a path of one of the light beams directed to one of the surfaces disposed relatively close to the deflector, wherein both of a section of the second light path before a first change of the second light path and a section of the second light path after the first change of the second light path intersect a section of the first light path after a second change of the first light path, and the first and the second light paths remain on one side of the deflector from which the first and the second light paths were deflected, respectively, the light scanning unit characterized in that: the deflector deflects other light beams from another side of the deflector to create third and fourth light paths in directions opposite to the first and the second light paths, respectively. the deflector deflects other light beams from another side of the deflector to create third and fourth light paths in directions opposite to the first and the second light paths, respectively.