PURPOSE: To prevent the generation of clogging in a vertical furnace and a ventilation fault.

CONSTITUTION: Cement raw materials, such as industrial waste, are pelletized by a pelletizing machine 1 to form green pellets P. These green pellets P are dried by a predrying machine 2 in common use as a horizontal type dust collecting machine to form the dry pellets P1. The dry pellets P1 are then calcined in a vertical packing type calcination furnace 5 to form the calcined pellets; thereafter, the calcined pellets are fired in a rotary kiln 20.