When a sheet is loaded to the sheet tray, the position of a trailing edge regulating section is set in response to the size of an insert sheet. Owing to this, the print sheet ejected from the ejection rollers onto the sheet tray falls onto the surface of the insert sheet. Further, when a booklet with an insert sheet placed therein is produced, an insert sheet is supplied to the sheet tray along the second conveying path. The shift amount of the execution position of center folding or the execution position of center stitching with respect to the sheet bundle is calculated in conformity to the finishing form of the booklet containing the insert sheet.