PURPOSE: To provide a gas turbine combustor capable of stable combustion by an ultra-low mixture of a fuel and air to reduce the production output of NOx, and of use of not only a gas fuel but also a liquid fuel.

CONSTITUTION: A combustor has a premixing zone 14 and a downstream combustion zone 10. The premixing zone 14 includes three concentric annular passages 30, 31, 32 provided around a central diffusion type dual fuel nozzle 33. Gas fuel manifolds 34, 35 are distributed along an annular passage 30 located inside a gas fuel and an outside annular passage 32. A plurality of dual fuel nozzles 38 are provided in the middle annular passage 31 so as to distribute the gas fuel or the liquid fuel along the middle annular passage 31 circumferentially. A dilute fuel air ratio is ensured with a circumferential fuel distribution along the annular passage, whereby production of NOx is reduced.