A hot metal supply injection method includes generating a negative pressure in a cylindrical container by a negative pressure generation device, and causing molten metal to be sucked into the cylindrical container from a retention furnace, while keeping an opening portion of the cylindrical container immersed in the molten metal, arranging the opening portion of the cylindrical container in a gate of a cavity while holding the negative pressure by closing up the opening portion of the cylindrical container after moving an inner plunger tip to a tip side of the cylindrical container, and moving the inner plunger tip to a rear end side of the cylindrical container, then moving an outer plunger tip, together with the inner plunger tip, to the tip side of the cylindrical container, and filling the interior of the cavity with the molten metal through injection via the gate.