PURPOSE: To obtain a long metal fine wire having a uniform circular cross section by specifying the ratio of length and diameter of a nozzle hole.

CONSTITUTION: The injection nozzle is provided with a crucible part 12 for melting metal or allay raw material, a nozzle part 13 for injecting the molten metal, an introducing hole 14 for charging the metal or alloy raw material into the crucible part 12 and a flange 15 for fitting the injection nozzle to an inert gas introducing part. The ratio value (l/d) of length (l) of the nozzle hole in the through hole from one end of the introducing hole 14 in the crucible part 12 toward the other end of nozzle part 13 in the crucible part 12 and diameter (d) of the nozzle hole 17, is made to be 5-10. By this method, the long metal fine wire having good circularity is obtd.