For improving characteristic uprising at the right-hand side of head-flow rate characteristic of a turbo machine, as well as for suppressing increase of vibration and/or noises thereof, a plurality of first grooves 24 in direction of gradient in pressure of fluid are formed on an inner flow surface of a casing, for connecting an inlet side of blades of an impeller and an area on the inner flow surface of the casing where the impeller blades reside in, over an inner circumference of the casing. Also, second grooves 25 in a circumferential direction are formed in an area on the inner flow surface of the casing where the impeller blades reside in, for communicating the first grooves in the circumferential direction of the casing.
This application is a continuation of U.S. Ser. No. 09/531,464, filed Mar. 20, 2000 U.S. Pat. No. 6,290,458, which is a continuation-in-part of application Ser. No. 09/399,132, filed Sept. 20, 1999 U.S. Pat. No. 6,302,643.
