A sheet processing apparatus which enable users to easily set the cutting amount of sheets according to the intended purpose of use. A folding unit folds the sheets. A cutting unit cuts off ends of the folded sheets. A setting unit sets details of processing of the sheets to be executed at least by the center-folding unit and the cutting unit. The setting unit is capable of selecting a first cutting amount-setting mode in which a cutting amount is set using a cutting width of the at least one end, and a second cutting amount-setting mode in which the cutting amount is set using a sheet size which the sheets should have after being cut. The setting unit sets the cutting amount in a selected one of the first cutting amount-setting mode and the second cutting amount-setting mode, when setting details of processing of the sheets to be executed by the cutting unit.