Abstract: A cylindrical boss hole 2a with a preferred tolerance is formed beforehand in the portion of a precision cast turbine blade unit 2, where it is to be joined to a rotor shaft 3. One end of the rotor shaft that has been finish machined beforehand is inserted into the hole 2a, and joint portions thereof are welded simultaneously by electron beam welding at a plurality of spots spaced at equal angles in the circumferential direction. Also, the turbine blades are machined using the outer periphery and the end surface of the previously finish machined rotor shaft as machining references. Thus, imbalances that are inevitably produced when using a conventional machining method can be greatly reduced, and the time needed to correct the imbalances is shortened and the yield of the products can be increased.