Abstract: This invention aims to offer an external heating rotary furnace for indirectly heating materials such as ore, coke, etc. which are liable to be oxidized, by insulating then from an oxidixing combustion gas atmosphere. The furnace comprises the following members: are reaction chamber (5) in which materials are heated to high temperature, defined by heat resistant ceramic means 4 from the combustion chamber (10) in which the fuel burns out.The fuel burns out in the combusion chamber, and combustion gas does not pass through the reaction chamber (5). Materials to be treated are heated indirectly in the reaction chamber (5) through the insulating ceramic wall (4).According to this invention, materials to be treated can be heated indirectly over 1,400.degree. C. effectively isolated from the combustion gas atmosphere, and inexpensive fuel can be used. Particularly, this invention is useful for the reduction of ores.