PURPOSE: To provide a molten magnesium supplying device where a piston ring is not required, the wear of an injection piston is less, a constant amount of the molten magnesium can be supplied, the molten magnesium is not left within the injection piston, and the maintenance in the overhaul operation is facilitated.

CONSTITUTION: An injection sleeve 5 which is a pressurizing chamber of the molten magnesium 8 and a molten magnesium supplying pipe 10 are arranged in a melting pot 3 where the inert gas is supplied. One end part 10a of the molten magnesium supplying pipe 10 is connected to the lower end part of the injection sleeve 5, and the other end part 10b is connected to a die casting sleeve 20. An injection piston 6 actuated by an injection cylinder 11 is slidably inserted into the injection sleeve 5, and the clearance (d) therebetween is set to 0.2-1.0mm. A communicating hole 13 to communicate the lower end part of the injection piston 6 with the inner and the outer parts is formed.