To produce a solid fuel from combustible waste materials at low cost and efficiently.

An intermediate-process product Q containing quick lime obtained by heating a cement raw material L is partly taken out from a cyclone 8 at the lowest stage of a suspension preheater in a cement baking system. The intermediate-process product Q as a treating agent is mixed to crushed combustible waste materials. The resultant mixture is subjected to treatments such as dehydration, sterilization and deodorization, and the treated combustible waste materials are molded to produce the objective solid fuel.