To efficiently supply a specified amt. of molten metal to an injection sleeve without the occurrence of inclusion of air into the molten metal.

The molten metal in a molten metal passage 45 is introduced into a molten metal housing space 73 while pushing up a check valve 77 in a molten metal reservoir section 19 by the downward actuation of a plunger 21 in a pump section 17. The molten metal is also introduced into outlet piping 93. When the actuation of the plunger 21 stops, the check valve 77 descends to a closed state and the molten metal in the molten metal housing space 73 and the outlet piping 93 is assured as it is and in this state, the molten metal is supplied to an injection plunger 3 again by the actuation of the plunger 21 on the basis of the molten metal surface A or molten metal surface B in the outlet piping 93.