PURPOSE: To obtain a fired product which contains an extremely small quantity of sulfur compound even if a combustion gas for heating contains sulfur.

CONSTITUTION: There are provided a preheating device 6 provided with an accumulation surface for receiving granular raw materials fed from the outside to form an accumulation layer 13 and a rotary furnace 1 which is in communication with the device 6 to receive the raw materials successively falling down to move the materials to a discharge part, while it is rotating, and a heating gas feed pipe 3 for feeding heating gas into the furnace 1 is fitted to a discharge part 1B of the furnace 1. And in a firing device wherein, after the heating gas has flowed from the furnace 1 toward device 6 countercurrently against the flow of the raw materials, the gas flows through the accumulation layer 13, a powder feed pipe 20 for spraying desulfurization powder from the outside is formed at an arbitrary position in a space extending from within the furnace 1 into the preheating device 6.