An image forming system which is comprised of a copying machine, and a sorter which has a bin assembly having a plurality of bins. In the sorter, the bin assembly is movable up and down pitch by pitch to store sheets on each bin, and stapled the stored sheets if necessary. A bin to store a first sheet and a first moving direction of the bin assembly are set in such a way that the bin assembly is stopped upward when the last process to sheets is finished.