A laser scanning unit is provided comprising a polygon mirror that deflects light beams respectively emitted by a plurality of light sources, an image focusing system that respectively focuses an image corresponding to each light beam deflected from the polygon mirror onto a surface of a plurality of photoconductive drums, and an incident optical system disposed between the light sources and the polygon mirror. The incident optical system comprises an infinite optical system along a main scanning direction and a finite optical system along a sub-scanning direction.