A production process of a gas turbine comprising a compressor for compressing atmospheric air and generating compressed air, a combustor for mixing and combusting the compressed air and fuel and generating combustion gas, and a turbine driven with the combustion gas, said gas turbine being constructed of a plurality of design elements necessary in designing said compressor, said combustor and said turbine, wherein the design elements of said gas turbine have parameters necessary in designing the design elements, and the process comprises: pre-selecting a compressor airfoil, a compressor rotor, the combustor, a turbine airfoil, a turbine rotor and a casing as common elements, which are used in common in various power generation cycles, from among the design elements of said gas turbine; pre-setting supplementary design items for the previously pre-selected common elements, which are points for which the gas turbine is designed and modified so as to make the common elements adaptable for the different power generation cycles, wherein the supplementary design items for the compressor airfoil and the compressor rotor include the increase and decrease of the number of stages and the replacement of material, the supplementary design items for the combustor include the presence or absence of a turbulence promoting rib and the replacement of material, and the supplementary design items for the turbine airfoil and the turbine rotor include the increase and decrease of the amount of cooling air, the presence or absence of cooling, the presence or absence of thermal barrier coating and the replacement of material; pre-setting at least one of the combustion temperature and the pressure ratio for each of the common elements, as parameters necessary for designing the design elements; setting set values of the parameters suitable for each of the common elements, based on optimum design conditions of the combustion temperature and the pressure ratio in the various power generation cycles; designing a gas turbine such that the common elements are adapted for a specific power generation cycle; adapting the common elements of the gas turbine to different power generation cycles by modifying the supplementary design items, when the set values of the parameters of the common elements differ from values of the parameters in the desired power generation cycle of the gas turbine to be produced; and producing the gas turbine. pre-selecting a compressor airfoil, a compressor rotor, the combustor, a turbine airfoil, a turbine rotor and a casing as common elements, which are used in common in various power generation cycles, from among the design elements of said gas turbine; pre-setting supplementary design items for the previously pre-selected common elements, which are points for which the gas turbine is designed and modified so as to make the common elements adaptable for the different power generation cycles, wherein the supplementary design items for the compressor airfoil and the compressor rotor include the increase and decrease of the number of stages and the replacement of material, the supplementary design items for the combustor include the presence or absence of a turbulence promoting rib and the replacement of material, and the supplementary design items for the turbine airfoil and the turbine rotor include the increase and decrease of the amount of cooling air, the presence or absence of cooling, the presence or absence of thermal barrier coating and the replacement of material; pre-setting at least one of the combustion temperature and the pressure ratio for each of the common elements, as parameters necessary for designing the design elements; setting set values of the parameters suitable for each of the common elements, based on optimum design conditions of the combustion temperature and the pressure ratio in the various power generation cycles; designing a gas turbine such that the common elements are adapted for a specific power generation cycle; adapting the common elements of the gas turbine to different power generation cycles by modifying the supplementary design items, when the set values of the parameters of the common elements differ from values of the parameters in the desired power generation cycle of the gas turbine to be produced; and producing the gas turbine.