A gas turbine combustor for mixing fuel into combustion air introduced from a compressor, burning an air-fuel mixture, and supplying produced combustion gas to a gas turbine. The combustor has a liquid fuel nozzle for jetting out liquid fuel and a pre-mixture chamber wall having a hollow conical shape gradually spreading in the direction in which the fuel is jetted out from the liquid fuel nozzle, and defining a pre-mixture chamber therein. A plurality of gaseous fuel nozzles are disposed around the pre-mixture chamber wall in an opposing relation respectively to a plurality of air inlet holes bored through the pre-mixture chamber wall and jet out gaseous fuel substantially coaxially with the axes of the air inlet holes.