To restrict the generation of NOx substantially by using a unique low NOx combustion method and an apparatus therefor.

A center axis-wise fuel jetting port 14 is provided to jet an auxiliary fuel in the direction of the center axis of the tip of a fuel pipe 1 and a disc plate 7 larger than the fuel pipe 1 is provided on the upstream side thereof. Air is jetted from a cylindrical air jetting part 18 for forming an air flow and a fuel from side part fuel jetting parts 5 and 6 is jetted at the right angle to an air flow jetted from a slot-shaped air jetting part 3 so as to make the fuel excessive at an excessive fuel jetting part 22 while making the air excessive at an excessive air jetting part. In this manner, variable density combustion is executed while making a mixed combustion. Ten(10)-20% of all the fuel is jetted from the center axis-wise fuel jetting port 14 in the direction of the center axis thereof to burn while making an internal furnace combustion gas flows as following wake. Thus, a ratio is not less than 0.2 between the air flow velocity at the slot-shaped air jetting part 3 and the fuel flow velocity at the side part fuel jetting parts 5 and 6.