An image processing apparatus which makes it possible to further simplify operations for designating a removable storage medium as a transmission destination of image data. A scanner section reads an image from an original. A controller unit transmits image data of the image input by the scanner section. A USB host I/F detects mounting and removal of the removable memory. The controller unit causes information concerning transmission to the removable memory to be displayed on the operating section in preference to information concerning transmission by another transmission method, according to detection of mounting of the removable memory.