To provide an image reading apparatus and its control method capable of matching both of the maximum size of an original readable by the image reading apparatus and the maximum size of paper sheet outputtable from an image forming apparatus even when they are different from each other in the case that a copy system is configured by connecting the image reading apparatus to the image forming apparatus.

A magnification reduction processing section 14 applies magnification processing to image data which are generated by an image read section 13 for reading an original. In this case, a carrying speed control section 16 controls a relative speed between an imaging element in the image read section 13 and the original.