To prevent lowering of pump efficiency by approaching the center of a swirl flow in a vortex pump 1 to the axial outer edge of a blade 3 to decrease an area inhibiting the air from returning to a blade passing part 18.

When the axial width of the blade 3 is taken as (a) and the distance between the axial inner wall of a fluid passage 2 and the axial outer edge of the blade 3 is taken as (b), the blade 3 is disposed in the fluid passage 2 to satisfy the relationship expressed by 0.60≤b/a≤0.76. Thus, although the center of the swirl flow separates from the axial edge part of the blade to be biased to the blade non-passing part in the conventional vortex pump, such biasing can be prevented not to lower the pump efficiency.