Patent ID: 7248377

Claim:
An image forming apparatus comprising: inputting means for inputting images; image forming means for forming images on blank sheets based on the input images; stacking means for stacking a plurality of bundles of insert sheets, wherein each bundle has insert sheets corresponding to n pages, which are to be inserted between the sheets having images formed thereon by said image forming means, in a predetermined order of pages in which the insert sheets corresponding to the n pages are to be inserted, and wherein the insert sheets corresponding to the n pages in each bundle are inserted in a single bundle of one copy set including the sheets having the images formed thereon by said image forming means; inserter means for feeding the stacked insert sheets so as to be inserted between said sheets having images formed thereon; reading means for reading identification information assigned to the insert sheets and generating an output indicating the read identification information; designating means for designating at least one insertion position in said sheets having images formed thereon for insertion of at least one of the insert sheets by said inserter means; detecting means for detecting based on the output of said reading means whether or not the insert sheet fed is for a top page in one of the bundles of insert sheets; and discharging means operable when said detecting means detects that the insert sheet fed by said inserter means after a printing start instruction has been given is not the insert sheet for the top page, for discharging insert sheets onto an escape tray until the insert sheet for the top page is detected by said detecting means.