To precisely detect molten metal surface level and to improve the responsiveness of the detection by detecting that the molten metal reaches the reference level, with an electric short circuit between an electrode body and an injection sleeve and stopping the supply of the molten metal after passing a prescribed time.

In a control for supplying the molten metal, the molten metal in a furnace at a fixed molten metal surface is supplied into an injection sleeve 13 through a nozzle 21 and a timer 36 is worked. When the molten metal surface level risen in the injection sleeve 13 reaches the reference level L1 and contacts with the electrode 41, the short circuit is electrically generated between the electrode 41 and the injection sleeve 13. A detected signal with this short circuit is given to a CPU 38. The CPU 38 measures the time from the level L0 to the level L1 with a timer 36, and this time is stored in a memory. After passing the prescribed time since the reach of molten metal to the reference level L1 is detected with a detecting sensor 40, the driving of the molten metal supplying device 23 is stopped through the CPU 38. Thereafter, a plunger tip is elevated and the molten metal supplied in the injection sleeve 13 is injected into a cavity in a metallic mold.