PURPOSE: To provide differential pressure countergravity casting capable of introducing an alloyant into molding metal for casting.

CONSTITUTION: A casting mold 7 having runners 62, 64 and a gate 16 and having a mold cavity 14 is placed on a drag slab 11 having a sprue 50 to be immersed into a molten metal pool and a reaction chamber 52. The alloyant (a fugitive element, such as Mg, can be included) 60 is housed into the reaction chamber. At the time of inhaling the molten metal 4 from the inside of the pool 2 by applying the difference pressure sufficient for upwardly sucking the molten metal through the sprue into the mold cavity between the mold cavity and the pool via a vacuum chamber 22 from a vacuum source 23, the molten metal flows into the reaction chamber where the molten metal is treated by the alloyant. The molten metal after the treatment flows into the mold cavity. The method is applicable to cast iron, aluminum, steel or the like.