The disclosure provides a gas turbine device capable of producing a mixed gas in which three or more types of gases are evenly mixed, and of doing the like. To achieve this, in a gas turbine device configured to burn in a combustor a fuel gas supplied from a fuel gas supplier, together with a compressed air supplied from an air compressor, and to rotationally drive a gas turbine by a combustion gas generated at the burning, the fuel gas supplier includes two mixers, and is configured to produce a mixed gas by mixing three types of gases of a first gas, a second gas, and a third gas in the mixers in ascending order of specific gravity or in descending order of specific gravity, and to supply the mixed gas to the combustor as the fuel gas.