To simplify a configuration of a curl straightening device to straighten a curl of a recording paper.

A laser printer 1 has a curl straightening unit 6 to straighten a curl of a paper sheet 3 on the downstream side of a fixing unit 23 in a conveying path of the paper sheet 3. The curl straightening unit 6 comprises a curl straightening unit 40 for cardboard which is arranged in the conveying path of the paper sheet 3 to straighten the curl of cardboard and a curl straightening unit 50 which is arranged on the downstream side of the curl straightening unit 40 for cardboard of the conveying path to straighten the curl of a regular paper. Thus, the curl of the cardboard or the regular paper can be straightened by only one conveying path. Further, the curl straightening unit 40 for cardboard and the curl straightening unit 50 for regular paper work as separate mechanisms, the control of switching the curl straightening mode according to the kind of the paper sheet 3 need not be performed. Thus, the configuration of the device can be simplified.