PURPOSE: To save the equipment cost and setting space by eliminating a holding pot and a pump.

CONSTITUTION: An inductor channel 12A and a throat part 11A are heated and dried and, by heating the inductor 12 with an induction heating device, an zinc ingot 21 is repeatedly supplied into the throat part 11A after the molten zinc 20 is filled up into the inductor channel 12A and the throat part 11A, and a part of the molten zinc 20 is repeatedly overflown into the furnace chamber 11 beforehand incorporating the zinc ingot 22 from the throat part 11A accompanied with the supply of the ingot 21. By heat of the molten overflown zinc 20, the ingot 22 in the furnace chamber 11 is heated and slowly melted, and also by the heat radiation from the molten overflown zinc 20, the wall surface of the furnace chamber 11 is made to dry.