PURPOSE: To eliminate the need for laminating blades for each stage and improve productivity by individually giving defined milling to the outer peripheries of rotor parts which are divided in the axial direction, and forming suction side and discharge side blades and, then, mutually joining said rotor parts.

CONSTITUTION: A rotor 1 is formed with rotor parts 1dW1f on which multistage blades 1aW1c having different helix angles are formed respectively. And, suction side blades are formed with the first blades 1a and discharge side blades are formed with the third blades 1c. Also, fit-in parts 1gW1j which are mutually fitted are provided on the rotor parts 1dW1f. Further, a rotary shaft 2 is fitted in the boss part 1K of the third rotor part 1f while boss parts 1KW1M are mutually fitted in by means of a bolt 3. And, milling is given individually to the outer peripheries of the rotor parts 1dW1f by means of straight cut-in cutting and circular interpolation cutting from the diametral direction and, after forming suction side and discharge side blades respectively, the rotor parts are mutually joined.