The guide vanes comprise two kinds of guide vanes which are alternately
placed in the circumferential direction of a shroud. One kind of the
guide vanes have a longer length than the other kind of the guide vanes,
in the region which is close to the surface of the hub, but have
substantially the same length as the other kind of the guide vanes, in
the region which is close to the shroud. The leading edges of the second
kind of guide vane are located further downstream in the pump axial
direction than the leading edges of the first kind of guide vanes.