PURPOSE: To reduce a discharging volume of non-ignited gas and restrict a generation of nitrogen oxide even if a discharged gas recirculation volume of a burner is varied in response to an amount of primary air by a method wherein porous red heater is arranged above a flame port surface of a Bunsen burner, a part of ignited discharging gas is guided from the porous red heater to a nozzle throat part and mixed with a primary air.

CONSTITUTION: Both fuel and primary air flowed into a burner 1 are ignited at a flame port of the burner, the formed flame heats a red heater 4 with its outer flame and cooled, then a part of it passes through the red heater 4 to form the secondary flame on it to perform a combustion and to make a substantial complete combustion of ignitable mixture gas. Simultaneously, the discharging gas formed inside the red heater 4 due to a negative pressure generated at a nozzle throat part 1a having a Venturi-shape, sucks it together with the primary air from a sucking port 8 through a discharging gas circulation passage 9 as well as through an aeration hole 7 to the nozzle throat part 1a so as to make a discharging gas circulation combustion. Therefore, a low combustion temperature is kept over an entire combustion area, so that it is possible to restrict a generation of nitrogen oxide.