PURPOSE: To ensure satisfactory combustion while suppressing generation of nitrogen oxides by interlocking a nozzle flame holder with a member supplying compressed air for forming a circulation region in a precombustion chamber by discharging a fluid oppositely to fuel flow thereby operating a burner also as a preheater.

CONSTITUTION: A first member comprises a supply source S1 of compressed air and powdered coal being carried by a duct 5 having an outlet in a precombustion chamber 6 extending into the combustion chamber 2 of a boiler 3. A second member comprises a supply source S2 of compressed air being carried by a duct 7. A tubular wall 9 is provided in order to form a wall 8 inclining in the direction of the combustion chamber 2 and the precombustion chamber 6 and to provide an annular opening 10. A rear wall 11 defines a chamber 12 coupled through the duct 13 of a third member comprising a supply source S3 of compressed air entering into the precombustion chamber 6 through the annular opening 1. A nozzle flame holder 14 receives combustion accelerating air through a duct 15 coupled with an air supply source S4 in the direction opposite to fuel flow from the outlet of a fuel transporting duct 5 and ejects air as shown in the arrow mark F.