A sheet post-processing device , comprising: a processing tray that accepts and loads thereon a prescribed number of sheets (P); a discharge tray that is disposed on a downstream side of the processing tray in a sheet conveyance direction, and onto which sheets (P) loaded on the processing tray are discharged; and a discharge roller pair that is composed of a discharge roller that comes in contact with an uppermost surface of sheets (P) loaded on the processing tray and a discharge roll that comes in contact with a lowermost surface of the sheets (P) loaded on the processing tray and that is rotatable only in such a direction as to discharge the sheets (P) onto the discharge tray , wherein a sheet (P) is discharged from the processing tray onto the discharge tray by forwardly rotating the discharge roller pair , and a sheet (P) is drawn in on the processing tray by reversely rotating the discharge roller in a state where the discharge roll is stopped from rotating, characterised in that the sheet post-processing device further comprises a roller holder that is swingable and rotatably supports the discharge roller , and the roller holder swings so that the discharge roller is selectively disposed at a retracted position away from the discharge roll and a contact position where the discharge roller comes in contact with the discharge roll , wherein the sheet post-processing device further comprises a biasing member that biases the roller holder downward, wherein in drawing in a sheet (P) on the processing tray , the discharge roller is disposed at the contact position by using only a self-weight of the roller holder , and in discharging a sheet (P) onto the discharge tray , the discharge roller is disposed at the contact position by, besides using the self-weight of the roller holder , biasing the roller holder downward using the biasing member. a processing tray that accepts and loads thereon a prescribed number of sheets (P); a discharge tray that is disposed on a downstream side of the processing tray in a sheet conveyance direction, and onto which sheets (P) loaded on the processing tray are discharged; and a discharge roller pair that is composed of a discharge roller that comes in contact with an uppermost surface of sheets (P) loaded on the processing tray and a discharge roll that comes in contact with a lowermost surface of the sheets (P) loaded on the processing tray and that is rotatable only in such a direction as to discharge the sheets (P) onto the discharge tray , wherein a sheet (P) is discharged from the processing tray onto the discharge tray by forwardly rotating the discharge roller pair , and a sheet (P) is drawn in on the processing tray by reversely rotating the discharge roller in a state where the discharge roll is stopped from rotating, characterised in that the sheet post-processing device further comprises a roller holder that is swingable and rotatably supports the discharge roller , and the roller holder swings so that the discharge roller is selectively disposed at a retracted position away from the discharge roll and a contact position where the discharge roller comes in contact with the discharge roll , wherein the sheet post-processing device further comprises a biasing member that biases the roller holder downward, wherein in drawing in a sheet (P) on the processing tray , the discharge roller is disposed at the contact position by using only a self-weight of the roller holder , and in discharging a sheet (P) onto the discharge tray , the discharge roller is disposed at the contact position by, besides using the self-weight of the roller holder , biasing the roller holder downward using the biasing member. <EOS>