To carry out the supply of a molten metal which dissolves the troubles brought with the high and the low supplying speeds of the molten metal, by gradually increasing and optimizing the supplying speed for forcibly supplying the prescribed quantity of the molten metal into a molten metal supplying hole of an injection sleeve in a casting machine.

At the time of transmitting a molten metal supplying start signal to a control device 25, a solenoid valve 70 is opened and a molten metal 17 in a molten metal discharging chamber 12 is energized and simultaneously, a proportional adjusting valve 40 is stroked to the upper side a little with a motor 50 through the control device 25 to slightly open a hole 19. When the molten metal 17 in the molten metal discharging chamber 12 veaches an injection sleeve 36 through the hole 19 and a molten metal supplying tube 30 with the pressure of an inert gas, the surface level of the molten metal 17 is gradually lowered. This surface level of the molten metal 17 is transmitted to the control device 25 and according to this surface level, the hole 19 is expanded by operating the proportional adjusting valve 40 with the molten 50 through the control device 25. When the molten metal 17 into the injection sleeve 36 reaches a prescribed amount, the injection is executed by a casting machine 35. Since the supplying of the molten metal 17 at an initial stage is executed at a low speed, the trouble such as spouting, is not generated and since thereafter, the supplying speed of the molten metal is gradually increased, the supplying time is shortened.