Patent ID: 7098938

Claim:
A multi-beam scanning optical apparatus comprising: incident optical means for making a plurality of light beams emitted from light source means having a plurality of light emitting portions incident on deflection means; and scanning optical means for forming images of the plurality of light beams deflected by said deflection means on a surface to be scanned, wherein said scanning optical means has at least one scanning optical element made of a resin, and said scanning optical element made of the resin has birefringence due to a stress distribution generated upon cooling in a molding process thereof such that the directions of principal axes of birefringence at one end portion of said scanning optical element made of the resin are different from those at the other end portion, opposite to said one end portion with respect to an optical axis thereof in a main scanning direction, of said scanning optical element made of the resin, and wherein an interval between adjacent scanning lines of scanning lines formed on the scanned surface by the plurality of light beams whose images are formed on the scanned surface through said scanning optical element made of the resin changes in the main scanning direction in an effective scanning region, and wherein said apparatus comprises at least one setting means for setting an interval error between scanning lines in a sub-scanning line direction, the interval error being caused by a relation in which polarization directions of the light beams emitted from the plurality of light emitting portions are not parallel or orthogonal with each other, to be not more than ⅕ of a desired scanning line interval.