Sheet processing apparatus and image forming apparatus having the same

An image forming apparatus, comprising:

• an image forming device which forms an image on a sheet;
• a stack portion on which sheets conveyed in a conveying direction from the image forming device are stacked;
• a first regulating portion which regulates a position of a sheet bundle, stacked on the stack portion, in a crossing direction crossing to the conveying direction by contacting an end of the sheet bundle stacked on the stack portion in the crossing direction;
• a second regulating portion which regulates a position of a sheet bundle, stacked on the stack portion, in the conveying direction by contacting an end of the sheet bundle in the conveying direction;
• a first binding portion which moves in the crossing direction so that the first binding portion moves from a first side of the image forming apparatus to a second side of the image forming apparatus and moves from the second side to the first side, and binds a corner portion of the sheet bundle by a staple, the corner portion including an end where the first regulation portion has contacted and an end where the second regulation portion has contacted, the corner portion being on the first side of the sheet bundle;
• a second binding portion which binds a corner portion of a sheet bundle without a staple, the corner portion including an end where the first regulation portion has contacted and an end where the second regulation portion has contacted, the corner portion being on the first side of the sheet bundle,
• wherein the second binding portion includes a first face having a plurality of projections and a second face having a plurality of concave grooves matching the plurality of projections, and
• the sheet bundle is bound by being nipped between the first face and the second face, and
• the sheet bundle is formed with a plurality of signs corresponding to the plurality of projections arranged side by side in a direction inclined to the crossing direction when the corner portion is bound by the second binding portion.