A post-processing device, comprising: a processing tray on which sheets are to be stacked; and a transport portion for transporting, toward the processing tray, a sheet introduced through an introduction port, the post-processing device being characterized by further comprising: a delivery mechanism for delivering the sheets stacked on the processing tray to a delivery tray on a boundary between copies, the delivery mechanism being configured to deliver, when a remaining number of sheets of one copy unstacked on the processing tray exceeds a maximum number of stacked sheets that is an amount of sheets stackable on the processing tray, a sheet bundle corresponding to the one copy a plurality of times so as to avoid delivery of only one sheet on a last page of the one copy; and a turn-aside portion for turning aside a sheet to delay arrival of the sheet at the processing tray, and then sending out the sheet to the processing tray, the turn-aside portion being configured to turn aside, when the remaining number of sheets of the one copy unstacked on the processing tray exceeds the maximum number of stacked sheets, a sheet on a first page to be stacked on the processing tray after delivering the sheet bundle. a processing tray on which sheets are to be stacked; and a transport portion for transporting, toward the processing tray, a sheet introduced through an introduction port, the post-processing device being characterized by further comprising: a delivery mechanism for delivering the sheets stacked on the processing tray to a delivery tray on a boundary between copies, the delivery mechanism being configured to deliver, when a remaining number of sheets of one copy unstacked on the processing tray exceeds a maximum number of stacked sheets that is an amount of sheets stackable on the processing tray, a sheet bundle corresponding to the one copy a plurality of times so as to avoid delivery of only one sheet on a last page of the one copy; and a turn-aside portion for turning aside a sheet to delay arrival of the sheet at the processing tray, and then sending out the sheet to the processing tray, the turn-aside portion being configured to turn aside, when the remaining number of sheets of the one copy unstacked on the processing tray exceeds the maximum number of stacked sheets, a sheet on a first page to be stacked on the processing tray after delivering the sheet bundle. a delivery mechanism for delivering the sheets stacked on the processing tray to a delivery tray on a boundary between copies, the delivery mechanism being configured to deliver, when a remaining number of sheets of one copy unstacked on the processing tray exceeds a maximum number of stacked sheets that is an amount of sheets stackable on the processing tray, a sheet bundle corresponding to the one copy a plurality of times so as to avoid delivery of only one sheet on a last page of the one copy; and a turn-aside portion for turning aside a sheet to delay arrival of the sheet at the processing tray, and then sending out the sheet to the processing tray, the turn-aside portion being configured to turn aside, when the remaining number of sheets of the one copy unstacked on the processing tray exceeds the maximum number of stacked sheets, a sheet on a first page to be stacked on the processing tray after delivering the sheet bundle.