To obtain a incombustible material, incombustible boards, and to provide a method for manufacturing them, which can effectively use disposed waste and which are light and has high incombustibility and, even if heated and burned, harmful gas is not generated and is safe and can be easily worked.

Crushed refuse 1 made of synthetic resin is fed into a water tank W, and in this water tank W, the crushed refuse 1 is agitated (20P), and settled matter 1A is removed from the water tank W (30P). The crushed refuse 1 which has been turned into suspended matter 1B is taken out from the water tank W (40P), and the crushed refuse 1B is cut, and is pulverized to granular substances (50P). To the crushed refuse 1 in the shape of granular substances, resource refuse 2 such as magazines containing vegetable fiber is added as an adhesive agent. Furthermore, when calcium silicate 3 and ammonium dihydrogenphosphate 4 are added and mixed (50P), the mixture is turned into incombustible material 5.