Patent ID: 7468823

Claim:
An optical beam scanning device, comprising: a light deflection device; a pre-deflection optical system which causes a light beam emitted from a light source to be incident to the light deflection device; and a post-deflection optical system which images the light beam, reflected from the light deflection device, onto a scanned surface, wherein an alignment surface to which the lens is fitted is located near a main scanning direction line passing through a midpoint of a maximum section thickness of the lens in at least one lens in one or the plurality of lenses constituting the post-deflection optical system, wherein the alignment surface to which the lens is fitted is located within the following range: 0.32 ≦Li/Lo ≦0.62 where Li is a distance between a vertex of an incident plane of said each lens and the alignment surface and Lo is a distance between a vertex of an incident plane of the each lens and a vertex of an outgoing plane of the each lens, wherein said each lens constituting the post-deflection optical system is made of plastic, wherein said each lens constituting the post-deflection optical system is formed by one lens, wherein a width in a main scanning direction of light flux of the light beam incident to the light deflection device is broader than a width in the main scanning direction of a single reflection plane of the light deflection device.