PURPOSE: To completely combust unburnt fine fuel and to prevent carbon from being accumulated on a wall surface, by a method wherein an annular groove is formed between an outer body and a main swirler for swirling main air for combustion, and a number of air feed holes are bored in the annular groove form.

CONSTITUTION: Main air for combustion produces a swirl flow through an air feed passage 13, formed between a combustor outer cylinder 1 and an end cap 11, with the air of a main swirler 15. A part of the main air is introduced through an air feed hole 17 communicated to an annular groove 16 formed between an outer body 3 and the main swirler 15, to the annular groove 16. Unburnt fine particles present in a region surrounded with the main air fed through an atomizing cone 18, formed in a manner to be spread approximately at 90° from the apex of a fuel valve tip 7, and the main swirler 15 by which to exert a swirl flow on the air for combustion is completely combusted to increase the temperature in a staying region 20 to 1,700°C or more. Through the utilization of the combustion heat, carbon is prevented from being accumulated on both side walls.