PURPOSE: To prevent the development of blow hole and the entrapment of coarse oxide by injection-casting molten metal in cavity after supplying reactive gas into the cavity while cutting off the communication of a pouring gate and a runner sprue.

CONSTITUTION: The molten metal 20 in a melting furnace 10 is introduced into a goose neck 11, and by pressing down with a piston 12, the molten metal is pressed into the cavity 18. As this preparation, a movable die 17 is set to a fixed die 16 and by advancing a flow divider 2, the sprue 14 is blocked with the tip part of the flow divider 2. By operating a reactive gas supplying means 4 and a control means 5, the reactive gas is supplied into the cavity 18 through the peripheral side of the flow divider 2. Further, the intrusion of the reactive gas into the goose neck part 11 is perfectly prevented. The supplying means 4 is stopped and the flow divider 2 is retracted to pour the molten metal into the cavity 18. The molten metal in the cavity 18 and the runner sprue 15 is taken out after solidification.