A gas turbine combustor of the pre-mixed combustion system in which the pre-mixed fuel and the air are combusted. The gas turbine combustor comprises main cylindrical nozzles provided in the end wall on the upstream side of a cylindrical combustion chamber, auxiliary nozzles formed to surround the main nozzles, a main pre-mixed gas supply for supplying a pre-mixed gas to the main nozzles, and an auxiliary pre-mixed gas supply for supplying a pre-mixed gas having an fuel/air ratio smaller than that of the main pre-mixed gas to the auxiliary nozzles, and wherein it is allowed to stably burn a lean pre-mixed gas having an fuel/air ratio of greater than 1 from a low-load condition through and up to a high-load condition of the gas turbine.