A decurl device includes: a curl detecting section having a plurality of toothed wheels each which detects a curling amount and a curling direction of a sheet having a curl; and a plurality of uncurling sections each arranged downstream of the curl detecting section in a conveyance direction of the sheet having the curl, which uncurls the sheet by bending and transforming the sheet in a direction reverse to a curling direction thereof. One of the uncurling sections, which reduces the curl, is selected on the basis of the curling amount and the curling direction that have been detected by the curl detecting section, thereby uncurling the sheet.