An image processing apparatus having multiple functions inputs image data for each of the multiple functions and stores the input image data in a memory. The image data stored in the memory is then processed. In the apparatus, a priority mode may be set in which a priority function is selected from among the multiple functions, and given priority to use a predetermined portion of the memory. A controller allows the predetermined portion of the memory to be used by the priority function only, when the priority mode is set, and allows the predetermined portion of the memory to be used by all of the multiple functions when the priority mode is not set.