PURPOSE: To provide the titled combustion chamber where the temperature near the oven top of flue and is raised and exhaust gas and the leaked gas from carbonization chamber side are brought into direct contact to carry out combustion the tar fraction in said leaked gas, thus leading the extension of oven life along with enhancement in working efficiency.

CONSTITUTION: A gas fed into the combustion chamber from a gas dispensing pipe 2 via the gas chamber 3 is mixed, in a flue 5 for combustion, with air fed from an air chamber 4 to carry out combustion. The resultant combustion gas is lifted through the flue 5, turning back at the communicating channel 8, then descending through the adjacent flue 5 followed by suction into a heat storage chamber, then being led to a small flue 13.