A duplex printing apparatus, comprising:
- printing means, which has a plate cylinder around which a duplex master is wrapped, the duplex master having two images of a first engraved image and a second engrave image formed next to each other along a direction of rotation of the plate cylinder, and pressing means capable of being attached/detached with respect to the plate cylinder in a relative manner;
- sheet feeding means for feeding a sheet toward the printing means;
- sheet discharging means for discharging a printed sheet printed by the printing means;
- sheet re-feeding means for temporarily holding a surface-printed sheet, the front side of which is formed with a printed image by the printing means so as to correspond to the first engraved image or the second engraved image, thereafter sending the surface-printed sheet to the pressing means, and turning the surface-printed sheet by means of rotation of the pressing means to re-feed the surface-printed sheet to the printing means;
- switching means for guiding the sheet, which has passed through the printing means, to the sheet re-feeding means or the sheet discharging means;
- and
- control means for controlling drive means of the sheet feeding means, printing means, sheet discharging means, sheet re-feeding means and switching means respectively, so that printing speed slows up from a low speed to a set speed when duplex printing is started,
- wherein, at the time of duplex printing, a first sheet is fed to the printing means by the sheet feeding means to perform, on the front side of the first sheet, surface printing corresponding to either one of the first engraved image and the second engrave image, thus obtained first surface-printed sheet on which printing is performed is guided to the sheet re-feeding means by the switching means, thereafter a second sheet is fed to the printing means by the sheet feeding means to perform, on the front side of the second sheet, surface printing corresponding to either one of the first engraved image and the second engraved image, and to re-feed the first surface-printed sheet to the printing means by means the sheet re-feeding means to perform, on the reverse side of the first surface-printed sheet, reverse printing corresponding to the other one of the first engraved image and the second engraved image, and thus obtained first duplex-printed sheet is guided to the sheet discharging means by the switching means, while thus obtained second surface-printed sheet is guided to the sheet re-feeding means.