PURPOSE: To stably and precisely supply the molten magnesium alloy to a diecast machine of cold chamber type.

CONSTITUTION: The supplying amount of the molten metal is precisely regulated by mechanically regulating the stroke of a piston 4 in a molten metal cylinder 3 dipped in a molten metal tank 2 by a nut 28 and a limit switch 30, and at the same time, a three-way valve 6 and a connecting block 5 provided with the delivery/discharge and suction passage and the molten metal suction passage 9 are connected to the cylinder 3, and the returning of the molten metal in a carrying guide tube 15 is prevented by the turning action of the three-way valve 6, and at the same time, the molten metal in the molten metal tank 2 is introduced into the cylinder 3. In other conditions of the three-way valve 6, the molten metal suction passage 9 is closed and the molten metal is supplied to the delivery passage 8 and the carrying guide tube 15.