To remove organic components by conducting the pretreatment which is the thermal decomposition of a raw material to form a workpiece, to effectively conduct the reformation of the workpiece by heat treatment in the next process, and to shorten the length in the shaft direction than a single rotary kiln to miniaturize equipment.

The workpiece obtained by removing organic components by the heating decomposition of the raw material is conveyed from conveying means 14, 48 into the rotary kiln 42 having multiply divided furnaces. In that time, the workpiece is dispersively introduced little by little into the divided furnaces 42a-42c, and the workpiece is reformed by heating and processing treatment while it is conveyed through the divided furnaces 42a-42c and then exhausted.