To efficiently treat waste rock wool and paper-making sludge which are waste difficult to treat and to reutilize them as a rock wool raw material.

The waste rock wool is compounded with the paper-making sludge with a solid weight ratio of 100:6 to 100. The mixture is kneaded, solidified and pelletized and a pellet is reutilized as a raw material to be charged into a melting furnace for manufacturing rock wool. As the waste rock wool, waste material occurred from a building overhaul site and waste material produced from a rock wool product manufacturing process are cited. As the paper- making sludge, the paper-making sludge discharged from a paper-making process in which recovered waste paper is utilized, is cited.