Patent ID: 7855815

Claim:
A document illuminating device comprising: a plurality of point light sources arranged in a main scanning direction; and a light guide optical system that guides a plurality of light beams emitted from the plurality of point light sources to a document surface, wherein the light guide optical system has: an entrance surface through which the plurality of light beams emitted from the plurality of point light sources enter; a plurality of curved reflecting surfaces that reflect the plurality of light beams having passed through the entrance surface and that are periodically arranged in the main scanning direction; and an exit surface through which the plurality of light beams reflected on the plurality of curved reflecting surfaces exit toward the document surface; and wherein each of the plurality of curved reflecting surfaces has a curvature in the main scanning direction, and an arrangement pitch of the plurality of curved reflecting surfaces periodically arranged in the main scanning direction is shorter than a spacing in the main scanning direction between the plurality of point light sources.