Centrifugal rotation machine

A centrifugal rotation machine comprising:

• a rotation shaft that rotates around an axis;
• a plurality of impellers that rotate along with the rotation shaft to send out a fluid;
• a casing that is installed to surround the rotation shaft and the plurality of impellers and defines a return flow channel configured to guide the fluid from the front-stage impeller to the rear-stage impeller;
• and
• a plurality of return vanes that are installed in the return flow channel at intervals in the circumferential direction of the axis,
• wherein the return flow channel includes a return bend section that guides the fluid, which has been sent out from the front-stage impeller to the outside in the radial direction, to the inside in the radial direction,
• wherein the return bend section includes a first curved portion and a second curved portion connected to the downstream side of the first curved portion, and
• wherein the radius of curvature of an inside wall surface of the second curved portion in the radial direction is greater than the radius of curvature of an inside wall surface of the first curved portion in the radial direction,
• wherein a leading edge of each return vane is located in the second curved portion of the bend section.