PURPOSE: To lower the evolution of NOx by elaborately effecting combustion in sections, thick-and-thin combustion, and selfrecirculating combustion.

CONSTITUTION: Air flows in an air pipe 13 as shown by arrows and forms numerous flows of vortices downstream from a rear plate 10 by virtue of rear blades 9 and rear air passages 8. From a rear gas hole 11 gas is ejected and drawn into the vortex flows and mixed favorably to produce a fuel-air mixture of lean gas. This fuel-air mixture mixes with other air favorably and makes stabilized, thin flames of its combustion, characteristic of a lean gas, on air passages 3. Gas ejected from a forward gas hole 7 impinges on the fuel-air mixture of lean gas ejected from an air hole 6 and mixes with it and further mixes with the fuel-air mixture of lean gas flowing out through the forward air passages 3, simultaneously with this mixing past the forward air passages 3 the mixture of the gas forms vortex flows as it flows downstream from a flame-holding plate 2. Through mixing favorably further thick combustion is effected. In this combustion the vortex flows draw in combustion gases around them so that effective recirculation of combustion is maintained.