Patent ID: 7087007

Claim:
A sheet post-processing apparatus for post-processing a sheet, comprising: conveying means for conveying a sheet stack in a conveyance direction; pushing means for pushing, at a predetermined position, the sheet stack in a direction substantially perpendicular to the conveyance direction ; and a pair of rotating bodies with smooth surfaces disposed adjacent to the pushing means and rotated in opposite directions for drawing therebetween the sheet stack pushed by the pushing means at a folding portion and folding the sheet stack, each of said pair of rotating bodies having at least two curved portions having different curvatures for drawing the sheet stack from a contact point between rotational shafts of the pair of the rotating bodies when the sheet stack is being folded, wherein the at least two curved portions comprise a first curvature portion having a first radius and a second curvature portion having a second radius less than the first radius, and join continuously around a periphery of the rotating body from the first curvature portion to the second curvature portion so that the sheet stack contacts the first curvature portions and then the second curvature portions and is folded between the first curvature portions and then between the second curvature portions.