PURPOSE: To lessen a machining work for both ends of a rotor by assembling the rotor into coupling brackets, with a projection from the inner diameter section of a bracket hole kept biting the rotor.

CONSTITUTION: Projections 30 and 31 formed on the inner diameter sections of brackets 22 and 23 are made to bite the external surface sections 24 and 25 of a rotor 21, thereby assembling the rotor 21 into the brackets 22 and 23. A revolving rotor composed of a blade and the brackets 22 and 23 coupled to the rotor 21, is fitted with a rotary shaft 10 via a bearing 11. The rotor so assembled is housed in a lower case. As a result, a structure ensuring the proper prevention of relative rotation is obtained almost dispensing with post- processing of both ends of the rotor 21 such as cutting. Thus, a problem can be eliminated, including the collapse of coupling state between the rotor 21 and the brackets 22 and 23 due to the fluctuation of a dynamic load acting on the blade during the rotation of the rotor 21, the sudden stoppage of rotation, and a dynamic load fluctuation due to the re-start of rotation or the like.