Finishing technology in image forming system

A finishing apparatus (FS), includes a stacker (72) for stacking recording sheets; a first conveyor for conveying a recording sheet sent from an image forming apparatus to the stacker; a sheet accommodating device (75) for accommodating a sheet (K) to be inserted at an insertion position which is at least one of the top of, the bottom of or a middle portion between the recording sheets; a second conveyor for conveying the sheet accommodated in the sheet accommodating device to the stacker; an input device for designating the insertion position of the sheet; a storing device for storing the insertion position designated by the input device; and a finishing controller for controlling the second conveyor so that the sheet is inserted into the recording sheets in accordance with the insertion position stored in the storing device.