In this study, it was examined the method to estimate equilibrium moisture content(EMC) at high vapor pressures and high temperatures above $100^{circ}C$. The material used for the experiment was Sugi(Cryptomeria japonica). EMC was investigated at temperatures ranging from $100^{circ}C$ to $160^{circ}C$ and under saturated vapor pressures above 1 atm. The correlation between temperatures and vapor pressures have a good agreement with those observed by thermocouple and pressure gauge in the air state of autoclave, respectively. A sensitivity of quartz spring was 65mm/g. Moisture content(MC)s calculated from the quartz spring elongation by vapor sorption showed a good agreement with MCs by oven-dried method. Using this system, it was found that EMC at high vapor pressures and high temperatures above $100^{circ}C$ were higher than EMC of wood in 1 atm pressure conditions. With this system, therefore, it was concluded that the EMCs of wood and wood-based materials at high temperatures were able to be evaluated.