PURPOSE: To prevent the chipping of the thin-walled parts at the parting by delineating part of the casting chamber forming the thin-walled parts of the casting by the specific movable core.

CONSTITUTION: After an upper die 1 and lower die 2 are coupled and clamped, molten metal is poured into a casting chamber 3 through a cross gate. At the stage when the molten metal has frozen, a movable core 5 which is movable in the die opening direction is first retreated and pulled off from the thin-walled part Wa. At this time, the stress along the moving direction of the movable core acts upon the thin-walled part, but there is no likelihood of causing chipping because said part is sandwiched by the upper and lower dies. Next, the upper die 1 is detached to open the dies, after which ejector pins 4 are ejected to part the casting W from the lower die 2.