To uniformize the firing of a ceramic-art formed body and to improve the combustion efficiency in the furnace by dividing a part of the flow of a high temperature gas, used for completely combusting an exhaust gas, from a high temperature gas main stream flowing into the inside of the furnace, allowing the divided steam to flow into a flue, placing at the bottom of the furnace, a part of the flue, that extends from the flow division point to an exhaust gas flow passage, and also placing an air introduction port for forming oxidizing flame, at a midway point of the part of the flue.

In this furnace, a mainstream of a high temperature gas introduced through a high temperature introduction port 16, is allowed to flow into the furnace inside 6 through a flow divider 19 and a furnace inside communicating hole 17, and used for firing a ceramic- art formed body. The exhaust gas formed in the furnace inside 6 is allowed to enter into a first flue 9 and concurrently, moved toward the high temperature gas introduction port 16 and further, allowed to enter into a second flue 11 and concurrently, delivered to an exhaust gas flow passage 12. Also, a part of the high temperature gas introduced is allowed to directly flow into a second flue 11 through the flow divider 19 and a flue communicating hole 18. When the high temperature gas has reducing properties, air introduced from an air introduction port 14 is added to the exhaust gas introduced from right and left communicating holes 10, to again combust the exhaust gas, to form oxidizing flame and to subject uncombusted matter in the high temperature gas to complete combustion before the high temperature gas reaches an exhaust gas communicating hole 13.