To improve ink acceptability of paper by giving proper water to the printing surface of a paper in the printing line to obtain good print reproducibility at a low printing pressure.

A paper humidifying device A that gives proper water to the surface of the printing paper is installed in front of a printing unit, and is composed of a humidification cylinder 1 having an aggregate of minute recesses 1B to accumulate a small amount of water from a water pail 2 on its surface, a doctor knife 4 for scraping extra water on the humidification cylinder 1, and a support cylinder 3 for supporting the printing paper (not shown) paired with the humidification cylinder 1. By making the printing paper pass between the humidification cylinder 1 and the support cylinder 3, the surface of the printing paper is humidified.