To provide an image scanner provided with an automatic document feeder that detects mixed original sizes, avoids occurrence of miscopy and degraded working efficiency even when a user forgets designation of a mixed loading mode wherein a size of recording sheet is automatically selected in matching with the size of each original, and assists the user to be able to set desired copying operations.

The image scanner detects the size of one original each, and displays an operation explanation picture of the mixed loading mode when the image scanner detects mixed loading of originals in the case that no mixed loading mode is designated.