A light scanning unit that includes: a light source unit for emitting first and second light beams; a beam deflector for deflecting the first and second light beams emitted from the light source unit; synchronization detection sensors for detecting scanning synchronization of the first and second light beams; and synchronization optical path converting members to deflect the first and second light beams toward the synchronization detection sensors. The optical paths of the portions of the first and second light are directed to come into close proximity with one another. The light scanning unit may be incorporated in an image forming apparatus.