PURPOSE:To make any trouble in copying paper to be fed afterward preventable before it happens, by selecting a selector device so as to feed the next copying paper into a discharge tray when detecting a fact that length of the copying paper during conveyance is more than the specified one. CONSTITUTION:When a duplex mode or a composite mode is selected, a central processing unit or a controlling device sets a selector claw 60 to an upper step position and opens a passage leading to the side of a paper refeed cassette 50. And, when a tip of copying paper out of a pair of paper discharge rollers 21 is detected by a sensor Se2, it starts a copying paper length detecting time. Next, when a rear end of the paper is detected by the sensor Se2, it judges whether crossfeed of an A4 format is or not by the copying paper length detecting timer, and if NO is the case, the selector claw 60 is selected to the lower step position by a solenoid 62, and the copying paper is conveyed to the side of a paper discharge tray 45 from the paper refeed cassette 50 for the exclusive A4 format cross feed. Thus any drawback such as a paper jam or the like due to the copying paper of more than the specified length to be fed in afterward is preventable before it happens.