PURPOSE: To increase the adjustment width of thermal power and to suppress the generation of carbon monoxide and odor by providing a plurality of flame holding plates formed and peripherally divided at the upper parts of inner and outer flame cylinders, and also providing a plurality of guide plates peripherally divided at the lower parts thereof.

CONSTITUTION: A flame holding metal fitting 9 is provided with a disk-shaped base body 10. A plurality of flame holding plates 11a and 11b formed protuberantly from the base body 10 and divided peripherally therefrom and at the further lower parts thereof, a plurality of guide plates 12a and 12b divided peripherally are protuberantly formed. An unburnt gas is sufficiently mixed with a high-temperature combustion gas in a joint gas flowpath formed between guide plates 12a, 12b and flame holding plates 11a, 11b and in a vortex flow formed on the flame holding plates 11a and 11b, oxidation is promoted and a combustion reaction is carried out, whereby carbon monoxide and hydrocarbon in unburnt components contained in the exhaust gas can be reduced and odor can also be reduced.