PROBLEM TO BE SOLVED: To reduce the generation of carbonic acid gas, to increase the safety of operation, and to increase quality.
SOLUTION: A combustion gas feeding part 1 is provided with an oxygen- hydrogen gaseous mixture generator 3, a carbon compound vaporizer 4 and a gas mixing chamber 5. The oxygen-hydrogen gaseous mixture generator 3 in the combustion gas feeding part 1 electrolyzes water to generate a gaseous mixture of oxygen and hydrogen. The carbon compound vaporizer 4 is used for stabilizing the flame of the oxygen-hydrogen gaseous mixture since the flame is not stabilized only in itself. The gas mixing chamber 5 mixes the oxygen-hydrgen gaseous mixture of the oxygen-hydrogen gaseous mixture generator 3 and hexane of the carbon compound vaporizer 4 so that their ratios reach a prescribed ratio, and feeds the resultant gaseous mixture into a gas burner 2.