A centrifugal compressor comprising: a rotating shaft, which rotates around an axis; a first casing which forms a cylindrical shape; a second casing which forms a cylindrical shape, is disposed on a downstream side of the first casing to be coaxial with the first casing, and has an outer diameter larger than an outer diameter of the first casing; a first impeller which is provided on the rotating shaft and disposed on a radially inner side of the first casing; a first return flow path which is disposed on a radially inner side of the first casing and guides a fluid flowing to a radially outer side from the first impeller toward a radially inner side; a second impeller which is provided on the rotating shaft, disposed on a radially inner side of the second casing, and connected to a downstream side of the first return flow path; an intermediate suction flow path which is disposed on the radially inner side of the second casing and additionally supplies the fluid to a flow path between the first return flow path and the second impeller; and a second return flow path which is disposed on the radially inner side of the second casing and guides the fluid flowing to the radially outer side from the second impeller toward the radially inner side, wherein: the first casing and the second casing are formed in a cylindrical shape extending along the axis; an outer diameter of the first return flow path is equal to or less than an inner diameter of the first casing; an outer diameter of the intermediate suction flow path and an outer diameter of the second return flow path are equal to or less than an inner diameter of the second casing; and the outer diameter of the intermediate suction flow path and the outer diameter of the second return flow path are larger than the outer diameter of the first casing. a rotating shaft, which rotates around an axis; a first casing which forms a cylindrical shape; a second casing which forms a cylindrical shape, is disposed on a downstream side of the first casing to be coaxial with the first casing, and has an outer diameter larger than an outer diameter of the first casing; a first impeller which is provided on the rotating shaft and disposed on a radially inner side of the first casing; a first return flow path which is disposed on a radially inner side of the first casing and guides a fluid flowing to a radially outer side from the first impeller toward a radially inner side; a second impeller which is provided on the rotating shaft, disposed on a radially inner side of the second casing, and connected to a downstream side of the first return flow path; an intermediate suction flow path which is disposed on the radially inner side of the second casing and additionally supplies the fluid to a flow path between the first return flow path and the second impeller; and a second return flow path which is disposed on the radially inner side of the second casing and guides the fluid flowing to the radially outer side from the second impeller toward the radially inner side, wherein: the first casing and the second casing are formed in a cylindrical shape extending along the axis; an outer diameter of the first return flow path is equal to or less than an inner diameter of the first casing; an outer diameter of the intermediate suction flow path and an outer diameter of the second return flow path are equal to or less than an inner diameter of the second casing; and the outer diameter of the intermediate suction flow path and the outer diameter of the second return flow path are larger than the outer diameter of the first casing. the first casing and the second casing are formed in a cylindrical shape extending along the axis; an outer diameter of the first return flow path is equal to or less than an inner diameter of the first casing; an outer diameter of the intermediate suction flow path and an outer diameter of the second return flow path are equal to or less than an inner diameter of the second casing; and the outer diameter of the intermediate suction flow path and the outer diameter of the second return flow path are larger than the outer diameter of the first casing.