To reduce a required memory capacity when reading an image of a plurality of originals and outputting the image.

During sort copy, a control section 9 generates multi-value image data from a plurality of images read by a scanner 1, a density conversion section 2 converts the multi-value image data into low density multi-value image data, a binarization section 3 converts the multi-value image data of low density into binary image data, which are stored in a memory 4 and sorted and printed out by a printer section 8.