To provide a method which appropriately adjusts the supply of damping water.

A first to a third detection patches 101-103 are used which are printed at positions close to each other on printed matter and show a difference in the density change of the printed matter between the patches, when the supplies of the damping water and ink are changed. The first detection patch 101 is a solid patch with a halftone density of almost 100%, the second and the third detection patches 102 and 103 are line pattern patches with a halftone density of (k×100)%, and the number of lines of each patch is different. The appropriate damping water quantity control can be performed by determining factors Nf and Nr by an Yule-Nielsen formula based on the measured densities Ds and Df of the first and the second detection patch and the measured densities Ds and Dr of the first and the third detection patch, and calculating the density factor of the water melted at an appropriate ratio.