Patent ID: 8026941

Claim:
A light scanning unit comprising: a light source unit for emitting light; a polygon mirror for deflecting and scanning the emitted light in a main scanning direction, the polygon mirror having a plurality of deflection surfaces and a plurality of edges at which adjacent deflection surfaces meet one another; an image forming optical system for condensing the deflected light; and a synchronization detection optical system for detecting a portion of light that is divided and reflected at an edge of the polygon mirror, wherein: the light source unit comprises first and second light sources being arranged such that light emitted from the first and second light sources are respectively incident on different deflection surfaces of the polygon mirror, the synchronization detection optical system comprises first and second synchronization detection units for respectively detecting, among light emitted from the first and second light sources and divided in two directions at each of different edges of the polygon mirror, light reflected at a deflection surface of the polygon mirror, and the first and second synchronization detection units are arranged diagonal-symmetrically with respect to the polygon mirror such that the first and second synchronization detection units respectively detect, among light emitted from the first and second light sources and divided in two direction at each of different edges of the polygon mirror, light reflected at a deflection surface of the polygon mirror, at which surface light to scan will be subsequently deflected.