PURPOSE: To prevent generation of vortex flow by arranging an inclined plane within an edge part area of an impeller blade directed toward at least an adjacent wall and arranging the inclined plane in a rotating direction of the impeller toward the wall.

CONSTITUTION: A back face 64 of each impeller blade 42 directed in the direction opposite to a rotating direction 58 has a bump-shaped member mounted on a plane which is substantially parallel to a plane 62 of a front plane and the member is restricted by three planes arranged so as to be different. The member is restricted by a second plane 68 connected with a first plane 66 toward an adjacent member, the plane 68 is arranged on the first plane 66 by being inclined to an adjacent wall 24 to 26 arranged perpendicular to a rotating axis 22 and is directed in the rotating direction 58. As a result, the bump-shaped member is tapered in the rotating direction 58 of an impeller 14 for an end face of the adjacent wall 24 or 26. As a result, formation of vortex flow is reduced and efficiency of a pump is improved.