PURPOSE: To prevent a rotor, when it rotates, from generating play between a rotor shaft part and a rotor part, by forming a turn stopper part in the peripheral of the rotor shaft part and the rotor performing an internal chill of the rotor part in this turn stopper part.

CONSTITUTION: A rotor 1 is formed by a rotor shaft part 2 and a gourd-shaped rotor part 3 which is mounted to this rotor shaft part 2 providing plural holes 3a. And the rotor shaft part 2 is formed by a long-sized rotor shaft part main unit 20, having an axial center Q, and supporting parts 21 positioned in both end parts of this main unit 20. Here the rotor shaft part main unit 20 forms along its axial direction interruptedly turn stopper parts 23 corresponding to constrictive parts in the rotor part 3. And the rotor 1 forms axial direction- stopper parts 24 between the turn stopper parts 23 further axial direction-stopper parts 25 also in both ends of the rotor shaft part main unit 20. In this way, the rotor 1 is prevented from generating play between the rotor shaft part 2 and the rotor part 3.