Centrifugal compressor and turbo refrigerator

A suction-and-discharge flow path includes a circumferential flow path that extends in an arc shape about an axis and an external communication path that is connected to both ends of the circumferential flow path. The circumferential flow path has a uniform flow path cross-sectional area in a circumferential direction, and a convex curved surface having a convex curved surface shape is provided between an outer peripheral wall surface of the circumferential flow path and a second inner wall surface of the external communication path. In a case where, when viewed in the axis direction, a curvature radius of the convex curved surface is defined as R and a radial dimension of the circumferential flow path is defined as W, a relationship of W≤R≤3W is established.