impinging jet a 2 to cool the wall surfaces thereof by the convection flow the impinging jet a 2 does not enter the combustor at the tail inner tube 13 but flows into the combustor as the combustion airs a 3 a 4 a 5 and a 6 of the premixing units 4 a 4 b 4 c and 4 d and as the combustion air a 7 of the pilot burner 3 at the small diameter inner tubes 1 a and 1 b corresponding to the first combustion chamber 2 a less than 20 of the combustion air a 1 flows into the combustor as a film cooling air to cool the inner surface thereof that is only cooling of the outer surface is conducted at the tail inner tube 12 so that the air to be used as a film cooling air can be used as combustion airs a 3 a 4 a 5 a 6 and a 7 thus increasing the amount of combustion air consequently a desired premixed fuel air ratio assuring a combustion temperature less than 1600 u00b0 c which ensures generation of no nox can be set and a reduction in the nox can thus be achieved the computing element 42 which performs the above described combustion method will be discussed as shown in fig1 premixed fuel flow rates w 1 through w 5 of the five stages are stored beforehand as functions relative to a gas turbine load in the computing element 42 for the five stages of fuel lines a total of the premixed fuel flow rates w 1 to w 5 is equal to a total fuel flow rate w 0 the premixed fuel flow rates w 1 to w 5 of the five stages are obtained by the.