Patent ID: 8493643

Claim:
A multi-beam light scanning apparatus comprising a plurality of scanning units each including: a light source unit including a plurality of light emitting portions arranged at intervals in a main scanning direction and in a sub scanning direction; an incident optical system which allows a plurality of light beams emitted from the plurality of light emitting portions to enter a deflection surface of a rotational polygon mirror; and an imaging optical system for condensing a plurality of light beams deflected by the deflection surface of the rotational polygon mirror on a scanned surface; and at least one reflection mirror in an optical path between the deflection surface of the rotational polygon mirror and the scanned surface, where: the deflection surface of the rotational polygon mirror and the scanned surface satisfy a conjugate relationship in a sub scanning section; the incident optical system in each of the plurality of scanning units allows a plurality of light beams to enter the deflection surface of the rotational polygon mirror at a finite angle from one of an obliquely upward direction and an obliquely downward direction with respect to a surface perpendicular to a rotation axis of the rotational polygon mirror in the sub scanning section; a difference between a first number of folds of the plurality of light beams entering the deflection surface of the rotational polygon mirror from the obliquely upward direction and being reflected by the at least one reflection mirror and a second number of folds of the plurality of light beams entering the deflection surface of the rotational polygon mirror from the obliquely downward direction and being reflected by the at least one reflection mirror is an even number; among a plurality of light emitting portions of the scanning unit that emit the light beams entering the deflection surface of the rotational polygon mirror from the obliquely upward direction, a first light emitting portion is defined to correspond to a first scanning line at a head in the sub scanning direction, while among a plurality of light emitting portions of the scanning unit that emit the light beams entering the deflection surface of the rotational polygon mirror from the obliquely downward direction, a second light emitting portion is defined to correspond to a second scanning line at the head in the sub scanning direction; and a height of the first light emitting portion in the sub scanning direction on the light source unit is different from a height of the second light emitting portion in the sub scanning direction on the light source unit, so as to reduce a deviation between the first scanning line drawn on the scanned surface and the second scanning line drawn on the scanned surface in the sub scanning direction.