The present invention is aimed at providing an image reading device that suppresses generation of a so-called edge shadow while suppressing uneven intensity of light emitted onto an original. A color copy machine 1 includes an illumination portion 347a that irradiates an original G with light. The illumination portion 347a includes a plurality of LEDs 501 disposed at predetermined intervals in a main scanning direction, an elliptical diffuser plate 507 that is disposed between the plurality of LEDs 501 and the original G and causes the light emitted by the plurality of LEDs 501 to diffuse, and a second reflection mirror 541B that reflects light, which is a portion of the light diffused by the elliptical diffuser plate 507 and not directly irradiated onto the original G, so as to irradiate the light onto the original G.