PURPOSE: To reduce noise from a pump without lowering of the pump performance by providing a groove between the outside circumference of the tip of vane and the front and rear face shrouds mating with said outside circumference.

CONSTITUTION: Provision of a groove 4 in the outside circumference of a vane will form an escape for the pressure when the vane 1 and casing tongue approach the most to each other, so that the width of pressure variation at this part will lessen. Because the blade's position in the rotational direction is a little displaced at the part with groove 4, a phase difference is generated in the time at which the blade 1 passes the tongue. For these reasons, the noise component due to the number of blades multiplied by the number of revolutions is reduced. Major part of the impeller's work is conducted by the central part of the blade 1 and the neighborhood of the shrouds 2, 3 has a small flux of flow because of influence of the walls, so that no drop of pump performance is brought about.