Sheet processing device and image forming apparatus

An image forming apparatus comprising:

• an image forming unit that forms an image on a sheet;
• a stacking unit that is used to stack a bundle of sheets that are placed upon each other with first edge portions of the sheets being aligned with each other, the sheets having images formed thereon by the image forming unit;
• a staple binding unit that binds the first edge portions of the bundle of sheets by driving a staple through the first edge portions, the bundle of sheets being stacked upon the stacking unit;
• a sheet binding unit that is provided integrally with the staple binding unit in a direction along the first edge portions of the bundle of sheets stacked upon the stacking unit, the sheet binding unit forming in the sheets a partially punched sheet piece having one portion thereof connected to the sheets, forming a cut in the sheets, and inserting an end portion of the partially punched sheet piece into the cut, to bind the first edge portions, wherein the sheet binding unit is a stapleless binding unit;
• and
• an angle changing mechanism that is capable of changing an angle of the staple binding unit with respect to the bundle of sheets when binding the first edge portions with the staple binding unit,
• wherein the angle of the staple binding unit with respect to the first edge portions when the staple binding unit binds a corner of each sheet is different from that when the staple binding unit binds a portion of each sheet other than the corner, and
• wherein the staple binding unit and the sheet binding unit are connected to each other so that an angle between the staple binding unit and the sheet binding unit is changeable, and wherein the angle changing mechanism rotates the staple binding unit to change the angle of the staple binding unit with respect to the bundle of sheets while maintaining the connection between the staple binding unit and the sheet binding unit.