PURPOSE: To enable self-breakage of a runner by arranging a circumferential notch in a rising runner of double bottom plates or adjusting thickness of the double bottom plates.

CONSTITUTION: A rising runner brick 26 having knife-edge-like circumferential projection 24 is arranged at the rising runner 10 of the double bottom plates 4. When molten metal is poured from a pouring runner 8 in this casting means to cast an ingot 12 in a mold 6, as the circumferential notch is formed in the rising runner 10 at the time of the solidified shrinkage of the ingot 12, the runner 10 breaks off itself by the stress concentration, based on shrinkaged strain. Next, in case of a straight type runner 10, the thickness of the double bottom plates 4 is adjusted to more than described value and then a tension strain worked to the rising runner 10 becomes greater than the breakage force of the runner 10, to break off the runner 10 itself. In this way, by the simple means and operation, the rising runner 10 breaks off itself.