In a conventional wave soldering bath, the bottom surface of a bath body in a position which is below the inlet of a duct underwent erosion by molten solder and had a hole formed therein, causing molten solder to be spilled out from the hole. The cause of erosion of the bottom surface of the bath body is a vortex (T) of molten solder formed below the duct inlet accompanying rotation of an impeller pump (10), and the vortex rubs the bottom surface of the bath body.In the present invention, a shielding member (14) is installed between the duct inlet (12) and the bottom surface (13) of the bath body such that the vortex is prevented from affecting the bottom surface.