Provided is a sheet processing device capable of preventing a folded sheet bundle from being opened after pressing to improve accumulating property and aligning property of the sheet bundle. A sheet processing device includes: a pair of sheet pressing members 70 that press a fold of a folded sheet bundle in a thickness direction of the fold; and a moving member 56 that moves the sheet pressing member pair 70 along the fold of the folded sheet bundle. The moving member 56 supports a plurality of rows of the sheet pressing member pairs 70 arranged in a moving direction of the moving member 56. The sheet pressing member pairs 70 press the folded sheet bundle with the intervals therebetween in the respective rows reduced stepwise in the moving direction of the moving member 56.