The guide vanes (3) comprise two kinds of guide vanes which are alternately placed around the angular direction. One kind of the guide vanes has a longer length than the other kinds of the guide vanes at the region which is close to the surface of the hub. However, at the region which is close to the shroud (4) the guide vanes substantially have the same length. The leading edges of the second kind of guide vanes are located further downstream of the pump axial direction than the first kind of guide vanes.
