This invention is directed to an image reading apparatus. In the apparatus, reading an original by irradiating it with light of three primary colors, respectively, and by receiving the reflected light is performed as follows. More specifically, an operation mode is designated, and conditions used to perform image reading are set in accordance with the designated mode. Under the set conditions, the image reading is performed according to a method of irradiating an original sequentially with beams of the three primary colors and reading the beams reflected by the original. Alternatively, under the set conditions, image reading is performed according to a method of irradiating an original simultaneously with beams of two primary colors in each of three different combinations of the three primary colors and reading the beams reflected by the original. Instead, image reading is executed twice according to these two methods.