To provide a centrifugal fluid machine capable of expanding stall limit in a diffuser to a low flow rate side, being stably operated over a wide flow rate range and minimizing decline in efficiency.

The centrifugal fluid machine is provided with an impeller having a plurality of blades and a hub arranged in root parts of the plurality of blades, and with the diffuser 21 provided in the downstream side of the impeller and having a plurality of vanes 24 between a shroud wall face 22 and a hub side wall face opposing to each other. On at least one of the shroud side wall face 22 and the hub side wall face, at least one groove 25, 25a extending from radial direction inner side faces 24a of the vanes 24 toward a radial direction inner side of the diffuser 21 and extending in a direction approximately vertical to the radial direction inner side faces 24a of the vanes 24 is provided.