An image reading apparatus includes a plurality of light sources to illuminate a document; an illumination optical system to guide light to a reading target area having a length and a width; a document illuminating device to illuminate the entire document; an image forming optical system to form an image from light reflected from the document; and a sensor provided in an image forming section of the image forming optical system to read the image of the document. The illumination optical system includes a concentration section to control light diffusion, and a reflection section. The reflection section includes at least two integrally configured reflection surfaces, in which a sine value of an angle of reflected light from at least one reflection surface is positive, while a sine value of an angle of reflected light from the rest of at least one reflection surface is negative.