Sheet processing apparatus, sheet processing method, and image forming system

An image forming system that includes an image forming apparatus and a sheet processing apparatus, in which sheets on which images are formed by the image forming apparatus are processed by the sheet processing apparatus, comprising:

• a receiver unit adapted to receive sheets discharged from the image forming apparatus;
• a center-folding unit adapted to fold the sheets at a center thereof;
• a cutting unit adapted to cut off at least one end of the folded sheets;
• a selecting unit adapted to select between a one-end cutting mode in which one end of the folded sheets opposite to a folded end thereof is cut off, and a multiple-end cutting mode in which a plurality of ends of the folded sheets except the folded end are cut off;
• and
• a setting unit adapted to set a cutting amount in a first cutting amount-setting mode in which a cutting amount is set using a length from the one end of the folded sheets, in a case where said selecting unit selects the one-end cutting mode,
• wherein said setting unit is further adapted to set the cutting amount in 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, in a case where said selecting unit selects the multiple-end cutting mode.