To provide an allay thin plate casting apparatus preventing an abnormal blow-off of molten metal and obtaining an amorphous alloy thin plate having a superior characteristics.

The amorphous thin plate casting apparatus is provided with a tundish having a nozzle, a molten metal supplying portion having a stopper for opening and shutting the nozzle, a pressure control portion controlling atmosphere in a tundish, and a cooling roll rapidly cooling and solidifying molten metal. The aforementioned pressure control portion is to decrease head pressure of molten metal applied to a gap between the stopper and the nozzle when the aforementioned stopper is under an opening motion. The head pressure of molten metal to the gap between the stopper and the nozzle is preferably increased step by step at the moment from the stopper opening to the starting of the molten metal pouring of the nozzle.