An object of the present invention is to improve an efficiency in using bins in a sorter of an image forming system, to which a plurality of personal computers are connected. If the number of the receptacles appointed in accordance with the receptacle appointment command or the number of sets of sheets to be sorted is larger than the number of empty receptacles, offset sorting is performed in which the position, at which the recording sheets are received, is shifted in the same receptacle. If the appointed number of the receptacles or the number of sets of sheets to be sorted is smaller than the number of empty receptacles, a normal sorting process is performed in such a manner that the bins are allotted in accordance with the position of the bins appointed with the command for appointing receptacles or the number of sets of sheets to be sorted.