A color image reading apparatus has a 3-line sensor formed by setting a plurality of line sensors on a single substrate, an imaging lens for imaging an object, a diffraction grating which is inserted in the optical path between the imaging lens and 3-line sensor and color-separates a light beam coming from the object into a plurality of color light beams, and a first cylinder unit which is inserted in the optical path between the object and the imaging lens, and temporarily images the object in the sub-scanning direction in the optical path before the imaging lens.