A flame produced within a premixer is promptly extinguished and a reduction in output power of a gas turbine associated with extinguishment is suppressed. In a gas turbine combustor including a diffusion burner and a premixed burner, the premixed burner is configured with a burner liner that surrounds the diffusion burner; a burner casing that surrounds the burner liner; a plurality of vanes that separate a cylindrical space between the burner liner and the burner casing into a plurality of premixers arranged side by side in a circumferential direction; a plurality of premixed fuel nozzles that inject a premixed fuel to the premixers; at least one thermometer installed to be buried in one of the vanes, and the like, and in a case in which a detection value of the thermometer exceeds a corresponding set value, an opening of each of premixed gas control valves is reduced and an opening of a diffusion gas control valve is increased in such a manner that a sum of flow rates of fuels supplied to the diffusion burner and the premixed burner remains unchanged.