PURPOSE: To provide a structure capable of realizing the long service life of a vane, and greatly increasing the period of the vane replacement.

CONSTITUTION: A vane 2 is divided by the cutting section having planes 10, 12 which are not parallel to any side surface so as to provide the variable width of the vane. In addition, a shaft on either of end faces of a rotor 1 is integrated with the rotor 1 to increase the length of a vane groove 3, or a flange 13 of a flanged shaft is abutted on and fixed to the end face of the rotor 1 without any shaft to support the rotor, and the vane groove is shifted to the center to increase the length, and the vane groove 3 is provided with a bottom part and the rotor 1 is not through from one outer circumferential surface to the other outer circumferential surface.