PURPOSE: To reduce NOx by making it possible to adjust the flow of primary and secondary air, providing a shut-off material between radiant tube and burner and controlling the volume of air flowing between burner and primary combustion inner cylinder.

CONSTITUTION: A suitablenumber of openings are provided on the circumference of primary combustion inner cylinder 5 provided in radiant bute 1 and burner proper 2. Here, damper 7 is provided and it controls the volume of flow of primary and secondary air. Cut-off material 9 is provided between tube 1 and burner 2, and it controls the volume of air flowing between burner 2 and inner cylinder 5. Fuel ejected from gas nozzle 3 is divided by damper 7 into primary and secondary. The fuel first reacts with primary air, and then it reacts with secondary air flowing outside of inner cylinder 5, and thereby the generation of NOx is greatly reduced.