To provide a method for producing high-strength lumber in which strength is raised without giving strain to tissue of lumber.

A pine tree is sawed and the sawed lumber is sufficiently soaked with water by soaking it in hot water. Water contained in tracheids 1 is forcedly discharged by irradiating microwaves and also cellulose tissue is softened. Then, while latent heat inheres, desirably within 60 seconds after irradiation of microwaves, lumber is compressed at pressure of about 2.5 tons by using a hydraulic press or the like so that volume of lumber becomes ≤30%; of original volume. Thereby, strain is not caused in tissue of lumber and also both strength and hardness are raised to about 30 times and tensile force is raised to about 10 times in comparison with raw lumber.