PURPOSE: To liberate a coating thickness by holding a molten metal in non- oxidizing atm., adjusting the contact conditions with a core wire by a nipple, die and stopper as well and passing the core wire through the molten metal.

CONSTITUTION: A nipple 3 and die 4 are provided at the lower part of the casting furnace 1 held in non-oxidizing atm. and the gap A between the nipple 3 and die 4 is made adjustable as well. A stopper 2 adjusts the flow of a molten metal 6 by its vertical movement. A core wire 8 is fed from the nipple 3 and the distance A between the nipple 3 and die 4 and the flow of the molten metal 6 are adjusted according to the conditions of the kind of a composite metal wire, joining speed, etc. The composite metal wire in an optional coating thickness is thus easily formed.