The seal devices on both ends of the rotary shaft are supported by the casing, the bearing on one end of the rotary shaft is supported by a bearing pedestal which is separated of the casing, the bearing on the other end of the rotary shaft is supported by the casing, the seal ring of the seal device on one end of the rotary shaft is divided into circumferential segments, and the seal ring of the seal device on the other end of the shaft is a unified seal ring.