PURPOSE: To eliminate thoroughly the failure in starting the supply of molten metal owing to clogging in a nozzle that arises frequently in the prior art by ejecting the molten metal charged from an intermediate tundish through a siphon into a nozzle tundish onto a cooling roll.

CONSTITUTION: Molten metal A' of the amt. sufficient for the succeeding operation is filled beforehand from a ladle 21 into a nozzle tundish 24 and an intermediate tundish 23. After the liquid level in the tundish 23 is maintained at the position where the required head in the tundish 24 is given, a siphon 29 made of refractories is put onto both liquid surfaces. The inside of the siphon 29 is connected with a constant pressure vacuum vessel and is quickly evacuated down to the prescribed pressure and is kept at said pressure, thereby communicating the molten metals between both tundishes. The opening/closing stopper 26 in the tundish 24 is then opened to charge the molten metal from a nozzle 25 onto a cooling roll 27, thereby producing an amorphous alloy light-gage strip B' of an Fe-B-Si-C alloy or the like. If the liquid level in the tundish 23 changes during this time, the tundish 23 is moved upward or downward by a lifting device 28 to maintain the liquid level in the prescribed position.