Patent ID: 8248445

Claim:
An optical scanning apparatus, comprising: a light source unit including a plurality of light emitting portions that are spaced apart from one another in a main scanning direction; a deflection unit for deflecting a plurality of light fluxes emitted from the plurality of light emitting portions for scanning; an incident optical system for guiding the plurality of light fluxes emitted from the plurality of light emitting portions to the deflection unit; and an imaging optical system for forming images of the plurality of light fluxes deflected for scanning by a deflection surface of the deflection unit on a surface to be scanned, wherein: the incident optical system includes an optical element including at least one noncircular optical surface in a main scanning section, and an aperture stop for restricting a light flux width at least in the main scanning direction of the light flux entering the deflection unit, which are disposed in the stated order from a side of the light source unit; the noncircular optical surface in the main scanning section of the optical element has a shape in which a positive power decreases from on axis toward off axis; and when a space between light emitting portions that are located farthest from an optical axis in the main scanning direction among the plurality of light emitting portions of the light source unit is denoted by W (mm), an optical path length between the aperture stop and an optical surface that is closest to the light source unit among the at least one noncircular optical surface of the incident optical system in the main scanning section is denoted by La (mm), a focal length of the incident optical system in the main scanning direction is denoted by f 1 (mm), and a light flux width in the main scanning direction of the light flux that is emitted from the light emitting portion which is located farthest from the optical axis in the main scanning direction on the optical surface closest to the light source unit among the at least one noncircular optical surface in the main scanning section of the incident optical system is denoted by D (mm), the following expression is satisfied 2 D≧|W·La/ 2 f 1 |≧D/ 8.