PURPOSE: To enhance the efficiency of double side copying and to improve the productivity by detecting number of original paper sheets, changing an original feed interval and sectioning a number of sheets in response to the copying mode and forming an image in the order of front and rear sides for each of the same number of sheets.

CONSTITUTION: An original rear detection unit SIRU selects either the both side read mode or the one-side read mode based on the result of detection a rear of an original. Then number of fed originals is detected and the original feed interval and the section number of sheets are controlled in the copying mode, the originals of a prescribed number of sheets is fed to a picture read section IRU and the front side picture is sequentially read. Then the rear picture of the original is read via a switch-back section SB and a re-feed paper path 58. Thus, a forming section 2 able to form the picture on both sides of the paper forms the picture on both front and rear sides of paper. Thus, the double side copying efficiency is improved.