To provide a sheet processing device and an image formation apparatus capable of stably ensuring a predetermined fastening force irrespective of conditions such as a surface property and a water content of a sheet.

A binding mode of a staple-free binding unit 102 for performing a binding process on a sheet bundle PA that is discharged to an intermediate processing tray 107 by sheet discharge means and that has one end abutting on a rear end stopper 108 by means of a pair of upper and lower teeth is switched over between a first binding mode of performing the staple-free binding process so that the paired upper and lower teeth ride over the sheet bundle PA and a second binding mode of performing the staple-free binding process so that the paired upper and lower teeth do not ride over the sheet bundle PA by mode switching means.