Patent ID: 8169673

Claim:
An illuminating device comprising: a linear light source mounted on a mounting surface of a board, with a plurality of light-emitting elements being arrayed thereon for irradiating light toward an illuminating target; a white reflecting surface provided in a planar shape parallel to an optical axis of the linear light source on a surface including the mounting surface, to reflect light from the linear light source; and a mirror surface formed in a planar shape that reflects the light from the linear light source and reflected light from the white reflecting surface, wherein when a surface including an optical axis of an imaging optics that images the reflected light from the illuminating target, and a row of pixels of a line sensor in which a plurality of pixels that convert the reflected light from the illuminating target imaged by the imaging optics to an electric signal and read an image on the illuminating target are arrayed in a main scanning direction is designated as a first plane, a surface including the mirror surface is designated as a second plane, a surface including the white reflecting surface is designated as a third plane, a region of space on one side where the linear light source and the white reflecting surface are arranged, using the first plane as a boundary, is designated as a light source region, a region of space on the other side where the mirror surface is arranged, using the first plane as a boundary, is designated as a mirror region, a first angle formed by the first plane and the second plane on the mirror region side and on the illuminating target side is designated as θ R , and a second angle formed by the first plane and the third plane on the light source region side and on the linear light source side is designated as θ W , the linear light source, the white reflecting surface, and the mirror surface are arranged such that the third plane crosses the first plane on the illuminating target side than the second plane, and 0°<θ W <θ R <90° is satisfied.