PURPOSE: To reduce discharge of NOx by providing a flame stabilizing ring with a first part projecting radially inward into a central passage, and a second L-shaped part projecting radially outward from a burner nozzle and receiving a retractable gas ejector.

CONSTITUTION: A flame stabilizing ring 118 blocks secondary air flow through an annular surrounded region 86 between a tubular burner nozzle 44 and a gas region sleeve 84. In case of coal firing, flame is combined on the inside of the ring 118 with regulated secondary air introduced through inner and outer annular passages and discharge of NOx is reduced. In case of oil firing, secondary air flow is influenced by the ring 118 and an air separation vane to reduce the quantity of oxygen for oil flame in the region immediately in the downstream of a burner port thus suppressing generation of NOx. In case of gas firing, flame is stabilized extremely because a retractable and turnable gas ejector 48 is shielded by the ring 118.