PURPOSE: To effect complete combustion and improve effects of decreasing NOx and smoke by a method wherein combustion gas is flowed in backwardly and induced into a high speed fuel jet.

CONSTITUTION: Four (4) pieces or less of air feeding tubes 13, 13', ... at tips thereof are provided around a periphery of a fuel nozzle 11 so as to be projected than the fuel nozzle 11 in order to feed combustion air, and peripheral spaces 14, 14', ... enough to flow in reversely the high temperature combustion gas toward center thereof from the periphery are provided between these air feeding tubes 13, 13', .... The high temperature combustion gas being flowed in reversely is induced into a high speed fuel jet and defused therein, thereby, effects heat absorbing gasifying reaction rapidly together with the fuel.