To provide a metal casting treatment method capable of suppressing cavities formed in a metal casting.

In the metal casting treatment method comprising a hot isostatic pressing stage where the metal casting is subjected to hot isostatic pressing, during the hot isostatic pressing stage (S12) and/or after the hot isostatic pressing stage (S12), a metal casting is immersed into a molten salt, and, the molten salt and the metal casting are relatively moved at a prescribed temperature in a vessel stored with the molten salt. Then, the molten salt and the metal casting are relatively moved preferably at a prescribed rate of 0.04 m/sec. As the metal casting, an aluminum alloy casting, a magnesium alloy casting or a titanium alloy casting is used.