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 (38, 39) arranged to position sheets stacked on the processing tray, the sheet positioning device (38, 39) 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 (38, 39) 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 (38, 39) 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 (38, 39) are to be bound and to a retracting position for retraction to an outside of sheets positioned by the sheet positioning device (38, 39); 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 (38, 39) arranged to position sheets stacked on the processing tray, the sheet positioning device (38, 39) 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 (38, 39) 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 (38, 39) 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 (38, 39) are to be bound and to a retracting position for retraction to an outside of sheets positioned by the sheet positioning device (38, 39); 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.