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, and the fold reinforcing unit includes a placement table on which the sheet bundle transported from the fold unit is placed, a band-like elastic member that is extended to face the fold line of the placed sheet bundle and is formed to be longer than the length of the fold line, and a roller unit that includes a reinforce roller and moves the reinforce roller along the direction of the fold line while pressing it to the fold line through the intervening elastic member.