PURPOSE: To enable an operation to continue without any trouble even when coating material peels and further to enable the operation cost and maintenance cost to be reduced.

CONSTITUTION: The transporting speed of a transporting device 9 installed at a rear stage of a rotary kiln 1 can be adjusted. There is provided a sensing means 11 for sensing peeling of coating material adhering to the inner surface of the rotary kiln. The transporting speed of the transporting device is adjusted by a control device 13 according to the result of sensing of the sensing means. As the sensing means for sensing peeling of the coating material, there are employed, for example, a measuring device for measuring the weight of the product discharged out of the rotary kiln, a wattmeter for measuring the electric energy of a driving motor for the rotary kiln or a wattmeter for measuring the electric energy of the driving motor for the transporting device.