Abstract: The invention aims to provide a lumber drying method which can dry lumbers in a short period without causing cracks and a lumber impregnation method to permeate processing agents deep into the lumbers at a low cost. The lumber drying method comprises a process to place lumbers in an airtight container and to heat them, a process to vacuum the inside of the airtight container, and a process to restore the air pressure after the vacuuming process. And, the lumber impregnation method comprises a process to heat lumbers, a process to place the heated lumbers under a vacuumed pressure, a process to immerse the heated lumbers in processing agents under the vacuumed pressure, and a process to restore the pressure of the lumbers immersed in the processing agents under the vacuumed pressure to the air pressure, and to immerse the lumbers in the processing agents under the air pressure.