A light scanning unit and an electrophotographic image forming apparatus are provided. The light scanning unit includes a light source emitting the light beams according to an image signal, an incident optical system including a flux-limiting element limiting the flux of light beams emitted by the light source, an optical deflector deflecting the light beams emitted by the light source in a main scanning direction, and an image forming optical system including a scanning optical element imaging the light beams deflected by the optical deflector on a scanning target surface, the light scanning unit forming an electrostatic latent image by scanning the light beams to the scanning target surface of the image bearing member. The scanning optical element of the scanning optical elements of the image forming optical system is eccentrically arranged from a central optical axis of the image forming optical system in a sub-scanning direction.