31 again into the primary passage 44 formed within the image forming unit 43 within the sheet reversing unit 41 are provided a pair of feed rollers 51 guide plates 52 and 53 which are positioned between the feed rollers 51 and guide plates 48 and curved guides 54 and 55 which provide a connection between the feed rollers 51 and the re feed unit 50 further for guiding the sheet which has passed through the fixing device 31 to the discharge tray 42 a change over pawl 56 is provided within the sheet reversing unit 41 so as to be pivotable between a close position in which it is kept away from the passage defined by the guide plates 48 as indicated by a phantom line in fig2 and a open position in which it projects into the passage defined by the guide plates 48 to close the passage for an image formed sheet in the case of forming an image on one side of the sheet only once or for a sheet which has been subjected to all of image forming steps in the case of forming images on one side of the sheet in plural number of times the change over pawl 56 is turned to the close position indicated by a phantom line in fig2 whereby the sheet is discharged onto the discharge tray 42 with the discharge rollers 47 on the other hand where there is made composite copying in which images are formed on one side of sheet in plural number of times the sheet is fed to the re feed unit 50 through the passage between.