Prior to reading an original image, whether to read the original image in a monochrome image mode in which the image reading apparatus reads the original image in use of the monochrome line sensor or a multi color image mode in which the image reading apparatus reads the original image in use of the multi color line sensor is predicted. Preparation of reading an original image based on parameters corresponding to the predicted mode is completed before the start of reading the original image. This arrangement reduces a time loss arising from switching of a color mode associated with a user color setting at the start of a job, and thus shortens the FCOT. This arrangement can shorten the time until the first copy is output after designating the start of copying when reading an original image based on different parameters.