A first seal member includes a double-structure bellows in corrugated form, and vibration control device provided on the outside of the bellows such as to cover part of the bellows. A flat portion that is not in corrugated form is provided in part of the bellows. The vibration control device is provided in circumferential direction on an outer surface of the flat portion, and made up of a ring-shaped rib having a plurality of holes in a circumferential direction and weights inserted in the holes provided in a wall of rib. Natural frequency is adjusted by adjusting the number of weights, thereby preventing resonance between the natural frequency of the first seal member and the rotational frequency of rotor from occurring.