To provide a fire retardant treated timber for protection of human life, while conventional interior building material for a living space burns rapidly in a case of a fire, causes spread of fire before fire-fighting activity, and generates combustion gas resulting in loss of human life, due to absence of legal obligation based on the difference in application of the fire law between an ordinary house building and a shop building where many persons gather.

Even with the recent development of technology, sprinkler installation from the ceiling of a conventional wooden house building based on legal obligation cannot solve the fundamental problems, though having some effect on initial fire. Although fire retardant treatment of timber is essential for thoroughly protecting human life from fire, the recent treatment of timber with fire extinction chemical hardly achieves fire retarding and may cause an accident resulting from toxic gas generation during fire. The fundamental fire retardation is preferably performed mainly with an inorganic agent, so that improvement in fire resistance and prevention of toxic gas generation can be achieved.