An image reading apparatus includes an integral scanning optical unit in which a light source device for illuminating an original placed on an original table, a plurality of mirrors for reflecting a light beam from the original and an imaging optical system for imaging the light beam reflected by the mirrors, upon a reading device, are integrally accommodated, wherein at least one mirror is so configured that the light beam is incident thereon twice or more, wherein, in a sub-scan section, reflection surfaces of the mirrors are disposed in a space at an original-reading-position side of a light entrance surface of the imaging optical system, and wherein the reflection surface of a mirror disposed at a position optically closest to the light entrance surface of the imaging optical system is placed at a position furthermost from the original table with respect to a direction of a normal thereto, as compared with the reflection surfaces of the remaining mirrors.