A first compression stage and a second compression stage being arranged at positions adjacent to each other. The first centrifugal impeller and the second centrifugal impeller are arranged in such an orientation that back sides of the first centrifugal impeller and the second centrifugal impeller face to each other. A connection flow path is formed in the first housing and the second housing for introducing the compressed fluid from the first compression stage into the second compression stage. An upstream portion of the connection flow path is formed integrally with the first housing, and a downstream portion of the connection flow path is formed integrally with the second housing.
