PURPOSE: To accelerate the growth in the preferential bearing of the crystal growth of an alloy and to produce easily a unidirectionally solidified casting having high quality by coating preliminarily a specific material on an investment shell mold for casting.

CONSTITUTION: A powdery and granular material prepd. by adding oxide of pentad metal, for example, antimony oxide Sb2O5 in a 0.1W10mol% range to titania TiO2 is coated on a casting mold. The mold is then calcined at a high temp. of ≥1,000°C in the atm. air to obtain an investment casting mold having high emissivity. The heat radiation of the casting mold is thus improved at a high temp. in a vacuum by which cooling capacity is improved and the increase in the temp. gradient of the solid-liquid interface in the stage of unidirectional solification is thus made possible. As a result, the growth in the preferential bearing of the crystal growth of the alloy is remarkably accelerated and the unidirectionally solidified casting having high quality is easily produced.