PURPOSE: To improve the stability of the molten metal supply quantity and the molten metal supply efficiency by using a pump for the molten metal.

CONSTITUTION: An outside driving device is connected with the pump driving port 6 of a pump 1 for molten metal through a hose, etc., and when the outside driving device is decompression-driven, the inside of an outer cylinder 2 is decompressed, and the check ball 3A of a check ball valve 3 is floated up simultaneously with the suction of the molten metal MN, and the check ball valve 3 is perfectly opened, and the molten metal MN is supplied into inside the outer cylinder 2. In this molten metal supply process, the floating up of the check ball 3A is regulated by a floating-up stroke regulating plate 7. When the outside driving device reaches the pressurization process, the plane of the molten metal MN supplied into the inside of the outer cylinder 2 is pressed, and further, the check ball 3A of the check ball valve 3 lowers from a stroke regulating plate 7, and closes the check ball valve 3, and in the case, the deflection of the check ball valve 3A for a valve hole 3B is exceedingly small, and the check ball valve 3 is put into a closed state, since the lowering time of the check ball 3A short and the lowering stroke is constant, and the leak of the molten metal MN is little, and the supply quantity of the molten metal MN is stabilized, and the molten metal supply efficiency is improved.