Patent ID: 8139998

Claim:
A sheet processing apparatus for processing a sheet or a sheet bundle, the sheet processing apparatus comprising: a notch part forming portion which forms a plurality of notch parts in an end part of a sheet or a sheet bundle, each notch part including a base part and an oblique side part that is cut off from the sheet on both sides of the base part; and a sheet binding portion which turns back the plurality of notch parts to bind the sheet or the sheet bundle, wherein the notch part forming portion includes a punch and a die, wherein a clearance between the punch and the die in a part parallel to the end part of the sheet bundle is set larger than a clearance between the punch and the die in a part where the notch is formed, and wherein each of the punch and the die has a blade for cutting the oblique side part, a blade surface of the punch has a gradient with respect to a blade surface of the die, and the blade of the die has an angle smaller than an angle of the blade of the punch.