PURPOSE: To enable manufacture of a large capacity machine suppressing maximum deflection of an impeller to a small level, reduce a sealing clearance between the outer circumferential surface of the impeller and the inner circumferential surface of a casing (reduction of leaking loss), miniaturize a device, reduce the weight of the device and employ an efficient working method such as broach working at the time of working of a rotor.

CONSTITUTION: A cylindrical surface body 13 having a cylindrical surface 12 which is in tight contact with the rotor outer circumferential surface of the rotor (the rotor of a bottom step side) of an engaging partner while projecting from the outer circumferential surface of a rotary center body 6, is formed on a part of the rotary center body 6 which corresponds to the axial direction intermediate position of an impeller 1, and also an impeller 1 is extended from the cylindrical surface 12 so as to connect integratedly the impeller 1 and the rotary center body 6 to each other. Each fixed hollow body 3 is extended from both end part sides of the impeller 1. At least the impeller 1 and a casing are made of light metal in the cylindrical surface 12 of the impeller 1 and the cylindrical surface body 13, and the rotary center body 6 is made of iron system metal.