A sheet finisher of the invention includes a saddle stitch unit configured to stitch a center of a sheet bundle in which printed sheets are bundled, a fold unit configured to fold the center stitched by the saddle stitch unit and to form a fold line, and a fold reinforcing unit configured to reinforce the fold line formed by the fold unit, the fold reinforcing unit includes a roller unit that includes a first roller and a second roller, and moves along a direction of the fold line while nipping and pressing the fold line of the sheet bundle transported from the fold unit by the first roller and the second roller, a drive unit configured to move the roller unit along the direction of the fold line from a standby position located at a position separate from an end of the sheet bundle, and a nip unit that includes a first nip plate and a second nip plate, and configured to nip the sheet bundle transported from the fold unit at a position between the fold line and the fold unit, and in the nip unit, the first nip plate and the second nip plate are opened in a thickness direction of the sheet bundle when the roller unit is located at the standby position, and the first nip plate and the second nip plate are closed to nip the sheet bundle when the roller unit reinforces the fold line after the sheet bundle is transported to between the first nip plate and the second nip plate.