Axial-flow type hydraulic machine

The present invention relates to an axial-flow type hydraulic machine, having an impeller of non-voluminous type therein, and in particular, to the machine being able to avoid falling into instability in flow, by suppressing pre-swirl generating in main flow of re-circulating flow at an impeller blade inlet and stalls due to blade swirls, thereby being suitable to be applied into an axial-flow pump and/or a reversible pump-turbine. In an axial flow hydraulic machine, a plural number of grooves are formed on an inner surface of a casing, directed into a pressure gradient direction, for connecting between an inlet side of an impeller and an inside of blade residing region on the casing inner surface. With movement of movable members provided on the casing inner surface, the grooves appear within the blade residing region in an unstable operation region, while the grooves cause no interference with the blades of the impeller in a stable operation region.