PROBLEM TO BE SOLVED: To reduce the liberation of an ink and a varnish in a pile of discharged printed sheets of paper by a face printing or double-side printing by a method wherein a drying device is disposed in an opening of the guide surface of a printed sheet guide system as a module, and the drying device is functionally combined with an air cooling system which is a separate body. SOLUTION: When a sheet of paper 5 is printed on one surface, the printed sheet 5 is dried by a drying device 10 which is operating. The pneumatic system 13 of a printed sheet guide system 9 which is disposed so as to correspond, is switched to a suction operation, and a cooling system 15 circulates cooling medium. When a drying device 18 is started, simultaneously with the heat transfer of the drying device 10 to the printed surface of the printed sheet 5, the rear surface which is not printed, is heated by the drying device 18 as well. At this time, fortunately, the temperature difference between the face surface and the rear surface of the printed sheet 5 is extremely small, and for this reason, in a pile of discharged sheets, the transfer of an ink or a varnish to the rear surface due to a heat transfer path, becomes drastically less.