A rotary-type fluid machine which enables practical and effective operation in an extremely low specific speed range. The rotary-type fluid machine (1, 1') has an impeller (10, 10') integrally connected to a rotating drive shaft (2). The impeller is accommodated in a casing (3). Fluid (a) of a suction fluid passage (4) to be pumped flows into a center part (11) of the impeller. The fluid (b) is discharged from a peripheral portion (12) of the impeller by the effect of the centrifugal force of the rotating impeller, so that the fluid is delivered through a delivery fluid passage (5) outside of the casing. Many grooves (15) extending toward a peripheral edge of the impeller from the center part of the impeller are formed on the impeller.
The groove opens on an outer circumferential surface (18) of the impeller, and causes strong recirculation vortices (R) to be formed in the vicinity of the peripheral edge of the impeller when the impeller rotates.