To simultaneously achieve the prevention of the casting failure and the reduction of the liquid metal loss, and produce the light castings with high reliability, excellent quality, and high precision at a low cost by improving the precision of heat transfer calculation during the low pressured aspiration, and considering the return of the liquid metal caused by the flow back into heat calculation after the low pressured aspiration stops.

Liquid metal is aspirated by reduced pressure from the bottom ward to upperward, and filled to a mold cavity. Four cavities 6 are connected to a riser 7 being connected to a runner 9 via a weir 8. The condition that all elements are filled with the liquid metal is called as the initial condition. The three dimensional shape of the mold for piping parts is mesh separated into an arbitrary hexahedron element and a triangle pole element. After the solidification analysis is performed in low pressured aspirating, the flowback and the solidification analysis are carried out until everything is solidified in a residual liquid metal range on the assumption that the liquid metal range connected to the furnace at for example 0.95 and more of the liquid phase rate goes back to the furnace when the low pressure aspiration is terminated, for predicting the residual liquid metal range in the flowback and the existence of the casting failure.