PURPOSE: To prevent pollution and to save energy consumption by decreasing NOX and O2, and by promoting uniform distribution of temperature in a furnace, by performing a wavy spray combustion.

CONSTITUTION: Fuel sprayed from a nozzle 6 repeats a period of much fuel and a period of little fuel many times within a very short time. This is so-called a wavelike spray, and the fuel is burned in thick and thin combustion. A minimum flow rate QM is always sprayed in order to hold ignition under a certain loading, and the number of spray times at the maximum flow rate QA within a specified time (T) is determined by the minimum flow rate. The time from the maximum flow rate to the next minimum flow rate, that is a wavy cycle time T1, is determined by the shape and the capacity of a furnace, the kind of fuel and the targetted value of NOX. When the final excess air coefficiency is determined as 1.1, for example, the generated value of NOX by this combustion method is as shown by A' in contrast to the value A of NOX generated by a conventional burner, and the difference E is the amount suppressed by this method in comparison with the case in a conventional burner.