There is provided a manufacturing method of a turbine casing capable of easily realizing improvement of reliability. A manufacturing method of a turbine casing according to an embodiment is a manufacturing method of a turbine casing which includes an outer casing formed of ferritic heat resistant steel and an inner casing disposed inside the outer casing and formed of austenitic heat resistant steel, and in which an exhaust hood to which a working medium after performing work in turbine stages is exhausted, is covered by the inner casing. Here, the inner casing is manufactured by using members produced by at least either forging or rolling.