To carry out drying of printing ink with the use of Nano sized high-temperature dryness steam. Nano sized high-temperature dryness steam being clustered on Nano oder is generated and jetted to the print side of printed material so that the Nano sized high-temperature dryness steam imparts intramolecular vibrational energy to ink of the print side. Consequently, the Nano sized high-temperature dryness steam being clustered on Nano oder not only passes through fiber pores in the printed material but also collides with the ink of the print side. The Nano sized high-temperature dryness steam having collided with the ink of the print side imparts thermally excited energy as intramolecular vibrational energy to the ink containing polar molecules. The ink is dried by the intramolecular energy.