A molten metal is poured into and stored in a hopper in a rotary-mold gravity casting process, so that a small amount of the molten metal is allowed to flow out of the hopper into a runner to previously fill up the runner. A casting mold is rotated from this state, thereby causing the molten metal to be filled from the hopper into a cavity by a difference in height generated between the molten metal level in the hopper and the molten metal level in the casting mold. Thus, when the molten metal, once stored in the hopper, is filled into the cavity in the casting mold by rotating the casting mold, the inclusion of air can be prevented from being produced due to ruffling of the molten metal in the cavity.