PURPOSE: To easily and surely manufacture a thin casting product by pouring molten metal at the specific flowing speed at the time of pouring the molten metal from casting hole in a sprue.

CONSTITUTION: For example, in the case of a mold 2 for small size boat body, such as motor boat, the mold is composed of a cope 2a and a drag 2b, and the sprue 1 is fitted to one side of the cope 2a. The sprue 1 is made to 2m height H from the max. height of the molten metal surface to the casting hole 1a in the case of casting. By pouring the molten metal from such height, at the time of pouring the molten metal from the casting hole 1a in the sprue 1, the pouring can be executed at ≥3m/sec flowing speed. In this result, even if this is the boat body having extremely thin thickness, this can be surely manufactured. Then, the flowing speed of the molten metal is made to the speed, which the molten metal flows out from a runner 3 to gate 4 after the time of pouring.