An incinerator has a furnace body whose height is 1.5-10 times the average internal diameter thereof. A combustion chamber is included which is formed by providing a plurality of air blast ports in a lower side wall and/or bank in the furnace body. A gas exhaust port is provided in the upper side of the combustion chamber and the side wall of the upper portion of the furnace body. A duct is included for leading an exhaust gas from the exhaust port to a place for making secondary use thereof.