Abstract: A device for preventing the leakage of a molten material remaining in the mold through the gate, the device including a specially designed valve members movable in opposite directions so as to effect the communication of the sprue with the mold and to form a negative pressure chamber therebetween, the negative pressure chamber being adapted to suck a molten material remaining in the mold whereby the internal pressure is vacated from the passageways in the mold. This prevents the molten material from leaking through the gate. When the negative pressure chamber is closed, the sucked molten material therein is expelled into the passageways.