To provide an Fe-Ni alloy ingot reduced in shrinkage hole and with good yield as a forging billet for a shadow mask.

A heat insulating means 6 housing an exothermic material 9 containing a metallic aluminum and an iron oxide into an opening hole vessel forming a Ti plate as the bottom part 7 and a heat insulating material as side walls 8 is preheated to ≥660°C, and just after completing the pouring of the molten Fe-Ni alloy into a mold 2, immediately, the preheated heat insulating means 6 is laid on a feeder head part 5. After laying the heat insulating means on the feeder head part, it is preferred to heat the lower surface of the Ti plate for 10min till 1450°C and thereafter, hold at 1425-1670°C.