A sheet decurling device includes a decurling conveyance part and a nip forming part. The decurling conveyance part includes a plurality of first rollers provided axially rotatably and a first belt wrapped around the first rollers. The nip forming part forms a nip part nipping and conveying a sheet with the first belt. The nip forming part includes a plurality of decurling rollers whose curvatures of outer circumferential surfaces are different from each other and a change-over mechanism. The change-over mechanism supports the plurality of de curling rollers axially rotatably and selectively changes over the decurling roller to be brought into pressure contact with the first belt.