A dual-fuel burning gas turbine combustor having a diffusive combustion burner to burn a liquid fuel and a gaseous fuel placed at the axis of the gas turbine combustor and a plurality of pre-mixing combustion burners to burn a liquid fuel and a gaseous fuel placed on an outer circumferential side of the diffusive combustion burner, each pre-mixing combustion burner having a liquid fuel nozzle, a plurality of gaseous fuel spray holes, a plurality of air holes, and a pre-mixing chamber to mix gaseous fuel and air, wherein each pre-mixing combustion burner has a double pipe sleeve at a connected portion between end cover and the pre-mixing combustion burner, and the double pipe sleeve has an inner sleeve having a gaseous fuel flow path, an outer sleeve positioned on an outer circumferential side of the inner sleeve, and a circular spacing formed between the inner sleeve and the outer sleeve.