A digital image forming apparatus arranges an image of a specified image document among a plurality of documents on a spread page located on the innermost side of saddle stitch type prints in gathering in easy operation with high reliability. The first backlighting medium is to conduct the first current and the second backlighting medium to conduct a second current. At each personal computer, the received signal is separated into its component parts by a VBI modem for display or control onof the personal computers.