a measurement section to measure the thickness of the stack of sheets a spine cover width determining section to determine a spine cover width in the cover sheet based on the thickness of the stack of sheets measured by said measurement section and an image forming section to form on the cover sheet a front cover image and a back cover image separating them by a spacing equal to said spine cover width application_number US 60435606 A description fig3 is a center cross section diagram of an image forming apparatus the image forming system has an image forming apparatus image forming section a and a binding apparatus binding section b the image forming apparatus a forms images on sheets using the electro photographic method and has an image forming section a 1 an original document conveying section a 2 and an image reading section a 3 in the image forming section a 1 a charging unit 2 an exposure unit 3 a developing unit 4 a transfer unit 5 a a separator unit 5 b and a cleaning unit 6 are placed around a drum shaped photoreceptor body 1 and each of the processes of charging exposure developing and transferring are carried out and toner images are formed on the sheets s 1 and the cover sheet s 2 the sheets s 2 that are the intermediate sheets when wrapped by the cover sheet s 2 if binding is done are stored in two sheet feeding trays 7 a and the cover sheets 32 are stored in the sheet feeding tray 7 b and in the cover sheet storage section 80 of the binding apparatus b one sheet each of the sheets s 1 and the cover sheet s 2 are.