Sheet finisher, image forming apparatus using the same, and sheet finishing method

摘要

A sheet finisher of the invention includes a saddle-stitching unit to stitch a center of a sheet bundle, a folding unit to fold the center and to form a fold, a first and a second rollers that move along a direction of the fold while nipping and pressing the fold of the sheet bundle and reinforce the fold, and a drive section to move the first and the second rollers along the fold from a standby position apart from an edge of the sheet bundle, and the first and the second rollers are separate from each other in a thickness direction of the sheet bundle at the standby position, and after the first and the second rollers reach to a position where they pass the edge of the sheet bundle of a processable maximum size, they come close to each other in the thickness direction and nip the fold.