A gas turbine production method for producing a derivative gas turbine of a different cycle based on a reference gas turbine including a reference compressor, charaterized by: letting a reference inner radius (d1-d6) and a reference outer radius (D1-D6) respectively represent an inner radius and an outer radius of an annular compressor channel of the reference compressor, an inner radius increment represent an increment in an inner radius of a compressor channel of the derivative gas turbine with respect to the reference inner radius, and an outer radius decrement represent a decrement in an outer radius of the compressor channel of the derivative gas turbine with respect to the reference outer radius, the gas turbine production method comprising the steps of: determining a compressor flow rate and a compression ratio required of a compressor of the derivative gas turbine; determining annulus areas required of the compressor of the derivative gas turbine based on the determined compressor flow rate and compression ratio; determining the inner radius increment and the outer radius decrement of an initial stage, determining the inner radius increment and the outer radius decrement of each of intermediate stages (36b-36e) on the downstream side of the initial stage such that the inner radius increment is not more than the inner radius increment of the previous stage and the outer radius decrement is not less than the outer radius decrement of the previous stage, and determining the inner radius increment and the outer radius decrement of a final stage on the downstream side of the intermediate stages (36b-36e) such that the outer radius decrement is not less than the inner radius increment under a condition that the outer radius of the compressor channel is decreased while increasing the inner radius of the compressor channel such that the annulus area of each stage of the compressor of the derivative gas turbine becomes equal to the determined annulus area, wherein the inner radius increment is determined to be greater than the outer radius decrement in the initial stage; designing the compressor of the derivative gas turbine by updating design data of components of the reference compressor that deviated from specifications due to the determination of the inner radius increment and the outer radius decrement such that the updated design data fulfill the specifications in the initial stage, in each of the intermediate stages (36b-36e), and in the final stage; and producing the compressor of the derivative gas turbine based on the design and thereby producing the derivative gas turbine. determining a compressor flow rate and a compression ratio required of a compressor of the derivative gas turbine; determining annulus areas required of the compressor of the derivative gas turbine based on the determined compressor flow rate and compression ratio; determining the inner radius increment and the outer radius decrement of an initial stage, determining the inner radius increment and the outer radius decrement of each of intermediate stages (36b-36e) on the downstream side of the initial stage such that the inner radius increment is not more than the inner radius increment of the previous stage and the outer radius decrement is not less than the outer radius decrement of the previous stage, and determining the inner radius increment and the outer radius decrement of a final stage on the downstream side of the intermediate stages (36b-36e) such that the outer radius decrement is not less than the inner radius increment under a condition that the outer radius of the compressor channel is decreased while increasing the inner radius of the compressor channel such that the annulus area of each stage of the compressor of the derivative gas turbine becomes equal to the determined annulus area, wherein the inner radius increment is determined to be greater than the outer radius decrement in the initial stage; designing the compressor of the derivative gas turbine by updating design data of components of the reference compressor that deviated from specifications due to the determination of the inner radius increment and the outer radius decrement such that the updated design data fulfill the specifications in the initial stage, in each of the intermediate stages (36b-36e), and in the final stage; and producing the compressor of the derivative gas turbine based on the design and thereby producing the derivative gas turbine.