A sheet processing device comprising: a processing tray on which a sheet is stacked; a processing unit which performs a predetermined processing on the sheet on the processing tray ; a discharge port through which the processed sheet is discharged; a discharge rollers pair having a lower roller provided in the discharge port and an upper roller facing the lower roller , the discharge rollers pair conveying the sheet on the processing tray ; a supporting arm which supports the upper roller and is provided to be turnable between a first position where the upper roller comes into contact with the sheet and a second position where the upper roller separates upwardly from the sheet; and an interlock mechanism which stops a performing of the processing by the processing unit when a turning of the supporting arm to the second position is detected, characterized in that the interlock mechanism includes: an actuator supported in the discharge port in a turnable manner and turned with an upwardly turning of the supporting arm ; a switch which detects the actuator to detect that the supporting arm is turned to the second position; and a switch moving mechanism which moves the switch to an actuator non-detective position and an actuator detective position, and the switch moving mechanism moves the switch to the non-detective position while the processing is not performed and moves the switch to the detective position while the processing is performed. a processing tray on which a sheet is stacked; a processing unit which performs a predetermined processing on the sheet on the processing tray ; a discharge port through which the processed sheet is discharged; a discharge rollers pair having a lower roller provided in the discharge port and an upper roller facing the lower roller , the discharge rollers pair conveying the sheet on the processing tray ; a supporting arm which supports the upper roller and is provided to be turnable between a first position where the upper roller comes into contact with the sheet and a second position where the upper roller separates upwardly from the sheet; and an interlock mechanism which stops a performing of the processing by the processing unit when a turning of the supporting arm to the second position is detected, characterized in that the interlock mechanism includes: an actuator supported in the discharge port in a turnable manner and turned with an upwardly turning of the supporting arm ; a switch which detects the actuator to detect that the supporting arm is turned to the second position; and a switch moving mechanism which moves the switch to an actuator non-detective position and an actuator detective position, and an actuator supported in the discharge port in a turnable manner and turned with an upwardly turning of the supporting arm ; a switch which detects the actuator to detect that the supporting arm is turned to the second position; and a switch moving mechanism which moves the switch to an actuator non-detective position and an actuator detective position, and the switch moving mechanism moves the switch to the non-detective position while the processing is not performed and moves the switch to the detective position while the processing is performed. <EOS>