To provide a sheet processing apparatus capable of shortening a time required to determine whether or not a sheet bundle has been normally stapled while suppressing an increase of an apparatus size and an increase of apparatus manufacturing costs, and capable of distinguishing sheet bundles not normally stapled from those normally stapled on a sheet discharge tray.

When the "absence" of a staple is detected in a sheet bundle by a staple detecting sensor, a paper discharge position on a paper discharge tray 137 is changed, and the sheet bundle is discharged after a sheet bundle is discharged which is discharged succeeding to the sheet bundle.