To provide a method for manufacturing worked lumber wherein worked lumber having sufficient flame retardance can be obtained by a simple process.

After providing a permeation hole in a lumber by laser beam machining, the lumber is permeated by a silicate compound solution containing alkali silicate, colloidal silica and the like. Thereafter, by liquefying acid anhydride gas (carbon dioxide and the like) into the silicate compound solution in the lumber, the silicate compound is allowed to gel. Thereby, the permeation hole can be easily provided in a higher precision than conventionally. Besides, since a higher impregnation rate is indicated and a permeation speed is larger in comparison with the lumber without providing the permeation hole, the permeation rate at least equal in quality thereto can be obtained in a processing time of about 1/2 to 1/40 time of the lumber without providing the permeation hole because of large permeation speed. Consequently, the permeation property and permeation efficiency of silicate compound are improved, and the modified lumber to which properties such as flame retardance and the like are imparted can be more effectively manufactured.