PURPOSE: To reduce the curl of a sheet after discharge efficiently and to improve transfer and separation during both-surface printing operation by closing a flow passage for supplying vapor to a recording member (sheet) when no paper is passed, and preventing a waste of vapor.

CONSTITUTION: An air flow is cut off by an elastic body 168 such as "Moltpren " at the upper part of a fixing device 16, so a convection current is generated, so that hot wind and vapor flows through a vapor passage 167 as shown by an arrow (a). The sheet 9 has the reverse surface exposed to the vapor passed through the flow passage 167 right after exiting from a discharge roll 17 to correct its curl, and the sheet becomes nearly flat when set in an intermediate tray, thereby improving stacking in the intermediate tray and separation from a photosensitive drum after the 2nd transfer. A plunger 170 is powered off after printing operation is completed, and a louver 171 is drawn by a spring 172 as shown by an arrow (c) to close the flow passage 167. When a both-surface copy is taken, the louver 171 is opened again as shown by an arrow (d). When recording operation is not performed, vapor is confined in the fixing device 16 to improve the ability in curl correction during the printing operation.