A method of operating a combustion apparatus, the combustion apparatus comprising: a combustion part provided with: a combustion space for generating a combustion gas by burning a combustible gas and air, a combustible gas inlet opened to said combustion space for allowing said combustible gas to flow into said combustion space, an air inlet opened to said combustion space for allowing said air to flow into said combustion space, and a combustion gas outlet for discharging said combustion gas outside; and an additional gas through channel part having an additional gas outlet for discharging an additional gas having a desired composition for adjustment of the composition of the combustion gas, said additional gas through channel part being adjacent to said combustion gas outlet and opened toward said combustion gas just after the combustion gas is discharged from said combustion gas outlet; wherein said combustion gas outlet and said additional gas outlet are such that the angle made by the discharge direction of the combustion gas from the combustion gas outlet and the discharge direction of the additional gas from the additional gas outlet is 5 to 90 degrees; and wherein the combustion apparatus has an inlet for said additional gas which is separate from said combustible gas inlet and said air inlet so that the additional gas can be introduced as a different gas from the air; the method comprising introducing a combustible gas via said combustible gas inlet to said combustion space and introducing air via said air inlet to said combustion space and burning the combustible gas and air therein, so that combustion gas passes out through said combustion gas outlet, and passing an additional gas, which is different from air, through said additional gas through channel part to said additional gas outlet in order to adjust the composition of the combustion gas. the combustion apparatus comprising: a combustion part provided with: a combustion space for generating a combustion gas by burning a combustible gas and air, a combustible gas inlet opened to said combustion space for allowing said combustible gas to flow into said combustion space, an air inlet opened to said combustion space for allowing said air to flow into said combustion space, and a combustion gas outlet for discharging said combustion gas outside; and an additional gas through channel part having an additional gas outlet for discharging an additional gas having a desired composition for adjustment of the composition of the combustion gas, said additional gas through channel part being adjacent to said combustion gas outlet and opened toward said combustion gas just after the combustion gas is discharged from said combustion gas outlet; a combustion part provided with: a combustion space for generating a combustion gas by burning a combustible gas and air, a combustible gas inlet opened to said combustion space for allowing said combustible gas to flow into said combustion space, an air inlet opened to said combustion space for allowing said air to flow into said combustion space, and a combustion gas outlet for discharging said combustion gas outside; and a combustion space for generating a combustion gas by burning a combustible gas and air, a combustible gas inlet opened to said combustion space for allowing said combustible gas to flow into said combustion space, an air inlet opened to said combustion space for allowing said air to flow into said combustion space, and a combustion gas outlet for discharging said combustion gas outside; and an additional gas through channel part having an additional gas outlet for discharging an additional gas having a desired composition for adjustment of the composition of the combustion gas, said additional gas through channel part being adjacent to said combustion gas outlet and opened toward said combustion gas just after the combustion gas is discharged from said combustion gas outlet; wherein said combustion gas outlet and said additional gas outlet are such that the angle made by the discharge direction of the combustion gas from the combustion gas outlet and the discharge direction of the additional gas from the additional gas outlet is 5 to 90 degrees; and wherein the combustion apparatus has an inlet for said additional gas which is separate from said combustible gas inlet and said air inlet so that the additional gas can be introduced as a different gas from the air; the method comprising introducing a combustible gas via said combustible gas inlet to said combustion space and introducing air via said air inlet to said combustion space and burning the combustible gas and air therein, so that combustion gas passes out through said combustion gas outlet, and passing an additional gas, which is different from air, through said additional gas through channel part to said additional gas outlet in order to adjust the composition of the combustion gas.