Disclosed is an image reading apparatus in which the amount of illumination light is increased and adverse influence of reflective illumination is reduced, and which is capable of reading image information of an original, such as a document, with high precision. The image reading apparatus includes an illuminating unit for illuminating image information of the original placed on an original support, and an image forming unit for imaging the image information on a reading unit. In the image reading apparatus, the illuminating unit includes a plurality of light source portions, the image information is read in a two-dimensional manner by changing a relative position between the image information and the reading unit, and the plurality of light source portions are disposed asymmetrically with respect to an optical axis of the image forming unit in a sub-scanning cross-sectional plane.