PURPOSE: To implement generation of lots of copies and generation of a single copy continuously without the operation of changeover of a sorter classification/ non-classification mode on each occasion by terminating the sorter classification when the end of classification is discriminated and executing continuously the image forming of originals left in an automatic original sender successively.

CONSTITUTION: The software such as calculation procedure, criterion and discrimination procedure is stored in a ROM 32, and a microcomputer 31 discriminates whether or not image forming is to be executed based on setting data called from the ROM 32 and picture data from a picture memory 29. That is, picture information is read from an original, a rate of change in a picture signal is obtained from the read picture information and whether or not the sorter classification is to be terminated is discriminated depending on the quantity of the rate of change. The rate of change in the picture signal is obtained by the total sum of absolute values of differences each resulting from subtracting a value of a center picture element from a value of surrounding picture elements of each division of a pattern sectioned into plural elements, and when the rate of change is smaller than a threshold level, it is discriminated that the classification is finished and the image forming is continued.