PURPOSE: To provide a metal mold casting method and its device, in which casting defect is not developed even not in high vacuum.

CONSTITUTION: In this die casting method, the molten metal 7 is filed up into a cavity 3 which is made to be in the condition of reduced pressure hydrogen atmosphere, and pressurized and solidified, and a hydrogen introducing means 5 for supplying the hydrogen into the cavity 3 is attached to the metallic mold casting device composed of a vacuum die casting device or a vacuum casting device. The reduced pressure hydrogen atmosphere is made by introducing the hydrogen into the cavity 3 and the molten metal 7 is filled up into there and pressurized and solidified. As the hydrogen is dissolved into the molten metal 7 in the high pressure even if the hydrogen is entraped in some degree, the casting defect is not developed. The high vacuum can be made to be the low vacuum by introducing the hydrogen, and the casting cycle time can be shortened.