In an image reading apparatus which can operate in a plurality of image processing modes, and includes a photoelectric converter for reading an object image and outputting an electrical signal, a reference white plate used to correct image read nonuniformity by the photoelectric converter, and a lamp for illuminating an object and the reference white plate with light, and its control, the currently set image processing mode is determined, a wait time is set in correspondence with the currently set image processing mode and the lamp is turned on, then the photoelectric converter begins to read the reference white plate after a lapse of the wait time.