PURPOSE: To ensure the release of very low contaminant, particularly the release of ultra low NOx by satisfactorily mixing a fuel and an oxidant to form a mixture of a fuel/oxidant, injecting the mixture of a fuel/oxidant into primary combustion apparatus chamber tangentially, and igniting them to combust a combustion product.

CONSTITUTION: To a primary combustion apparatus chamber wall 17 there is coupled at least one nozzle 13 having an outlet end communicated with a primary combustion apparatus chamber 11. A mixture of a fuel and air passes through a nozzle 13 having a nozzle outlet 19 communicated with the primary combustion apparatus chamber 11 and is injected into the primary combustion chamber 11. The nozzle 13 is coupled such that a spiral 16 is added to the mixture of a fuel and air and a combustion product produced owing to combustion of the mixture in the primary combustion apparatus chamber 11. The primary combustion chamber 11 is substantially cylindrical, and is communicated is fluid coupling with the secondary combustion apparatus chamber 12.