A wave soldering tank includes a soldering tank body for housing molten solder and a solder feed chamber disposed within the soldering tank body. An axial-flow, multiple-blade screw-type pump is disposed so as to draw molten solder into the solder feed chamber through an inlet and discharge the molten solder through an outlet. In a preferred embodiment, the pump includes a rotatable hub and a plurality of helical blades secured to the hub at equal intervals in the circumferential direction of the hub, each of the blades overlapping an adjoining one of the blades when the blades are viewed in the axial direction of the impeller.