A pump includes a pump unit, a pump case, a motor unit, a plurality of guide blades forming plural guide paths in tangent directions of the impellers; and a multiplicity of return blades to form paths for collecting the liquid under pressure from the guide paths into a suction opening of a next-stage impeller. The return blades have a configuration in which a total cross sectional area of inlet openings of concave paths formed by a plurality of ribs is set to be equal to or larger than a cross sectional area of the suction port, while a total volume of the concave paths is set to be smaller than the total volume of non-path portions excluding the paths.