PURPOSE: To enable to manufacture extremely low-carbon steel, while accelerating degasifying reaction, when molten steel is vacuum-degasified and decarburization-refined by RH degasifying process, by making the depth of the molten steel at the side of the ascending pipe of immersed pipes of a vacuum vessel smaller, and making that of the molten metal at the side of the descending pipe larger.

CONSTITUTION: The vacuum vessel 1 of RH degasifying apparatus is located with inclination to a supporting frame 8, so that the depth of molten metal inside the vacuum vessel is made smaller as h1 at the side of an ascending pipe 2 but larger as h2 at the side of a descending pipe 3. Since the depth of the molten steel at the side of the ascending pipe 2 is smaller, splashes 11 of the molten steel are sufficiently formed in the vacuum vessel. Since the molten steel is deeper at the side of the descending pipe 3, the staying time of the molten steel is longer. By these two actions, the ability of degasifying the molten steel is improved, decarburizing reaction by the degasification is accelerated, and the production of extremely low-carbon steel can be easily performed.