A fold-enforcing assembly comprising: a fold-enforcing device including: a pair of pressing members configured to nip and press a fold of a sheet bundle in a direction of thickness of the sheet bundle; a pressing mechanism configured to pressurize and depressurize the pair of pressing members in the direction of thickness; and a driver configured to drive the pressing mechanism ; a moving device configured to move the fold-enforcing device in a direction of the fold; and a control circuit configured to: move, with the moving device , the fold-enforcing device in accordance with a size of the sheet bundle in the direction of the fold; pressurize, with the pressing mechanism , the pair of pressing members in the direction of thickness, to press a first end portion of the sheet bundle in the direction of the fold; and move, with the moving device , the fold-enforcing device to a second end portion of the sheet bundle opposite the first end portion in the direction of the fold; characterized in that the control circuit is further configured to: depressurize, with the pressing mechanism , the pair of pressing members in the second end portion. a fold-enforcing device including: a pair of pressing members configured to nip and press a fold of a sheet bundle in a direction of thickness of the sheet bundle; a pressing mechanism configured to pressurize and depressurize the pair of pressing members in the direction of thickness; and a driver configured to drive the pressing mechanism ; a pair of pressing members configured to nip and press a fold of a sheet bundle in a direction of thickness of the sheet bundle; a pressing mechanism configured to pressurize and depressurize the pair of pressing members in the direction of thickness; and a driver configured to drive the pressing mechanism ; a moving device configured to move the fold-enforcing device in a direction of the fold; and a control circuit configured to: move, with the moving device , the fold-enforcing device in accordance with a size of the sheet bundle in the direction of the fold; pressurize, with the pressing mechanism , the pair of pressing members in the direction of thickness, to press a first end portion of the sheet bundle in the direction of the fold; and move, with the moving device , the fold-enforcing device to a second end portion of the sheet bundle opposite the first end portion in the direction of the fold; characterized in that the control circuit is further configured to: depressurize, with the pressing mechanism , the pair of pressing members in the second end portion. move, with the moving device , the fold-enforcing device in accordance with a size of the sheet bundle in the direction of the fold; pressurize, with the pressing mechanism , the pair of pressing members in the direction of thickness, to press a first end portion of the sheet bundle in the direction of the fold; and move, with the moving device , the fold-enforcing device to a second end portion of the sheet bundle opposite the first end portion in the direction of the fold; characterized in that the control circuit is further configured to: depressurize, with the pressing mechanism , the pair of pressing members in the second end portion. <EOS>