Abstract: According to the present invention, in the PFC (planar flow casting) method, He gas at room temperature is blown onto the surface of a cooling roll at a flow rate of 0.1 to 5 liters/min.multidot.cm.sup.2 through a He gas blow nozzle provided upstream of a molten alloy (a puddle) ejected through a molten alloy ejection nozzle onto the surface of the cooling roll at a distance from the ejection nozzle, the distance from the surface of the cooling roll and an angle of inclination of the nozzle within respectively specified ranges, thereby forming a He gas atmosphere around the puddle, and a thin strip is dragged out of said puddle. This enables a thin amorphous alloy strip having a very small thickness and a smooth surface free from significant uneven portions and pores to be easily produced at a low cost without use of any vessel for regulating the atmosphere or an apparatus for heating the blown gas.