To perform the massive disposal of waste by extending the application range of recycling resources.

The recycling of the waste is performed by manufacturing a lightweight building structural material having excellent heat resistance and refractory property by combining a carbide produced from combustible waste with by product gypsum recovered by plant stack gas treatment. The flame retardancy of the material is improved by incorporating the carbide obtained from the waste in a gypsum board and an inorganic material such as gypsum or aluminum hydroxide in a carbide board.