To restrain variation in the thickness of an R-T-B based alloy which has occurred in the conventional strip casting method.

An invented tundish includes a body having a slant section and a flat section which form a flow passage of molten metal, a lid placed oppositely to the flat section with a prescribed space formed between the lid and the flat section, and a heating means set on the lid. An invented method includes a step of manufacturing the molten R-T-B-based alloy by heating raw materials charged into a crucible so as to make the alloy of prescribed chemical composition and a step of rapidly cooling the molten R-T-B-based alloy charged to a cooling roll of which the surface roughness Ra is 1.2 μm or more via the tundish with the space functioning as a charging gate so as to manufacture the R-T-B-based alloy of which the standard deviation of thickness is extremely small in comparison with that of the conventional alloy.