PURPOSE: To prevent the nozzle from being blocked by cooling the nozzle part by a part of whole combustion air.

CONSTITUTION: Steady temperature air of 2W20% of the whole combustion air is supplied from an air nozzle 16 between air nozzles 20 for supplying pre-combustion air through a cooling air supply port 18 in the periphery of a central oil nozzle 14 for supplying fuel oil. On the other hand, by operating an operating handle 29 to open a cock of an oil adjusting mechanism in a predetermined amount, and oil is supplied from an oil supply port 15 to an oil nozzle 14. In this manner, cooling air of 2W20% of the whole combustion air quantity constantly flows to the outside of the oil nozzle 14 to cool and protect the oil nozzle 14. Hence, even when oil of heavy quality is used as a fuel oil and its supply amount is decreased or turned OFF, oil is not carbonized within the oil nozzle 14 and does not block the nozzle.