An image reading apparatus equipped with an illuminating device having little tint variation. A lamp unit illuminates an original with light, and includes a plurality of white LEDs, and a plurality of auxiliary LEDs that emit lights of different colors and arranged in a manner associated with the white LEDs. A CPU causes auxiliary LEDs to be lighted, so as to correct a color of light emitted from each of the white LEDs. An image reading unit reads the original illuminated by the lamp as an image.