PURPOSE: To prevent the leakage of molten metal from the bottom surface of a mold and obtain purified metal in good yields by cooling the molten metal to be refined in the mold from the bottom part of the mold while oscillating a plate- like body finely in vertical directions within the molten metal.

CONSTITUTION: The molten metal 2 to be refined such as Al is put into a mold 1 and while it is kept at adequate temp. with heaters 3, air or the like is blown to a purified metallic ingot 4 through cooling pipes 5 from the bottom part of the mold whereby the metal is cooled. While the purified metal is crystallized successively at a solidification interface 6 by this, the molten metal 2 is flowed upward through the through-holes 8 of an oscillator 7 which oscillates the molten metal finely in vertical directions as it is operated by an oscillation motor 9. More specifically, the molten metal 2 is passed through the inside of the holes 8 provided to the oscillator 7 in vertical directions to form impulsive flow against the rugged surface of the interface 6 and is flowed further upward. As a result, the concd. solute (e.g.; Fe, Si) is diffused into the upper molten metal, and the purified metallic ingot is obtained in good yields.