PURPOSE: To burn fuel gas under unbalanced condition and restrain the generation of NOx accompanied by the combustion by a method wherein a combustion air discharging port and a fuel discharging port are arranged in the radial direction of a radiant tube so as to be apart from each other by arranging the combustion air discharging port and/or the fuel discharging port eccentrically.

CONSTITUTION: Fuel discharging ports 3 are provided at both ends of a radiant tube 2 and are connected to a hydrocarbon gas fuel pipeline. Air discharging ports 4 are provided at both ends of the radiant tube 2 and an air sending facility as wall as an exhausting facility are connected thereto to serve both for air feeding and exhausting. When either one end port functions as an air feeding port, the other end side port functions as the exhausting port. The fuel discharging port 3 is formed so as to have the shape of a slit in order to mix the fuel with air in a high speed while the air discharging port 4 is provided with a circular shape in order to increase self circulating stream and both of them are arranged in a positional relation of being part from each other. In this case, the fuel discharging port 3 and the air discharging port 4 are arranged eccentrically.