A sheet binding processing apparatus, comprising: a discharging roller which discharges a sheet in a sheet discharging direction; a processing tray arranged to stack sheets discharged by the discharging roller ; a sheet positioning device arranged to position sheets stacked on the processing tray , the sheet positioning device including a sheet end regulating device and a side edge aligning device , the sheet end regulating device performing regulation with abutting against a sheet tailing end of a sheet in the sheet discharging direction, the side edge aligning device positioning a sheet side edge in a direction perpendicular to the sheet discharging direction; a first binding device which includes a first binding portion and a second binding portion arranged at a position distanced from the first binding portion by a first predetermined distance and which is arranged to bind a tailing end, of the sheet discharging direction, of sheets positioned by the sheet positioning device by nipping the sheets with the first binding portion and the second binding portion; a second binding device which includes a third binding portion and a fourth binding portion arranged at a position distanced from the third binding portion by a second predetermined distance being shorter than the first predetermined distance and which is arranged to bind a tailing end, of the sheet discharging direction, of sheets positioned by the sheet positioning device by nipping the sheets with the third binding portion and the fourth binding portion; a driving device (74, M3) arranged to move the second binding device to a binding position where the sheets positioned by the sheet positioning device are to be bound and to a retracting position for retraction to an outside of sheets positioned by the sheet positioning device ; and a controller arranged to control the driving device (74, M3) and to cause the second binding device to be located at the retracting position when the first binding device binds sheets. a discharging roller which discharges a sheet in a sheet discharging direction; a processing tray arranged to stack sheets discharged by the discharging roller ; a sheet positioning device arranged to position sheets stacked on the processing tray , the sheet positioning device including a sheet end regulating device and a side edge aligning device , the sheet end regulating device performing regulation with abutting against a sheet tailing end of a sheet in the sheet discharging direction, the side edge aligning device positioning a sheet side edge in a direction perpendicular to the sheet discharging direction; a first binding device which includes a first binding portion and a second binding portion arranged at a position distanced from the first binding portion by a first predetermined distance and which is arranged to bind a tailing end, of the sheet discharging direction, of sheets positioned by the sheet positioning device by nipping the sheets with the first binding portion and the second binding portion; a second binding device which includes a third binding portion and a fourth binding portion arranged at a position distanced from the third binding portion by a second predetermined distance being shorter than the first predetermined distance and which is arranged to bind a tailing end, of the sheet discharging direction, of sheets positioned by the sheet positioning device by nipping the sheets with the third binding portion and the fourth binding portion; a driving device (74, M3) arranged to move the second binding device to a binding position where the sheets positioned by the sheet positioning device are to be bound and to a retracting position for retraction to an outside of sheets positioned by the sheet positioning device ; and a controller arranged to control the driving device (74, M3) and to cause the second binding device to be located at the retracting position when the first binding device binds sheets. <EOS>