PURPOSE: To enable the suitable casting planning and mold designing by executing a test casting into a wedge shape test casting space preformed with a metallic mold and a sand core.

CONSTITUTION: In the metallic mold 1 as an outer frame, the wedge shape test casting space 4 making the top side at the lower part and the bottom side in the opening part at the upper part is arranged. While keeping in contact with the one side of the test casting space, a sand core 7 having rectangular parallelepiped or the wedge shape for making the top side at the lower part and the bottom side in the opening part at the upper part is inserted and the test piece having the wedge shape cross section is cast preceding to casting of a product. The casting structure of the test piece is detected to inform the condition of the casting structure in the metallic and sand combined mold. In this way, the condition of cooling and solidification in the molten metal is systematically and quantitatively observed, and behavior of the molten metal to the metallic mold and the sand core can be informed.