Turbo machines

A turbo machine, comprising:

• an impeller;
• and
• a casing accommodating said impeller therein, wherein:
• a plural number of first grooves are formed on an inner surface of said casing, opposing to an outer periphery portion of said impeller on an inlet side, in a periphery direction, connecting between a place where re-circulation flow occurs when being low in flow rate and an area where the blade tips exist on an inner surface of said casing,
• a second groove portion is formed on the inner surface of said casing, in vicinity of an inlet of said impeller, being declined to a peripheral direction;
• and further, and
• said second groove portion is communicated with said first groove portions, and is provided at a position, so that fluid having pressure necessary for suppressing a pre-swirl from occurring in main flow in an upstream side of said impeller can be taken out therefrom.