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, nips the fold line of the sheet bundle transported from the fold unit between the first roller and the second roller, and moves along a direction of the fold line while pressing, and 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 the first roller and the second roller are separate from each other at the standby position, and approach each other to nip the fold line in a region where the fold line of the sheet bundle exists.