PURPOSE: To measure accurately and with high precision a moisture content even if such content is higher than a fiber saturation point by containing an electrolyte in wood and measuring said content of wood by a DC resistance moisture content meter.

CONSTITUTION: A single plate of wood is dyed usually to a suitable color before pressure adhesion, in this time, an electrolyte is added in a dyeing vessel to treat the single plate simultaneously with the dyeing or an electrolyte solution is impregnated singly to the single plate. As the electrolyte, e.g. NaCl, Na2SO4, etc. can be used. In such a way, since the single plate containing the electrolyte contains water, the electric resistance variation is caused suddenly. The variation of the value indicated in the DC resistance moisture content meter corresponds accurately to the moisture content variation of the single plate, an accurate calibration curve can be prepared, and even the moisture content of the single plate higher than the fiber saturation point can be measured with high precision.