In a process for vacuum refining a molten steel wherein a refining flux is used, a fuel gas and an oxygen gas are spouted into the outlet of a top-blown lance of a vacuum refining apparatus to form a burner flame below the top-blown lance, and, at the same time, a refining flux is fed into the top-blown lance with the aid of an oxygen gas as a carrier gas and further passed through the burner flame, and the heated and melted refining flux is allowed to arrive at the surface of the molten steel. In this case, the refining flux feed rate and the circulating flow rate of the molten steel during vacuum refining are regulated so as to have a predetermined relationship, achieving a low flux consumption throughout a period of single refractory life of the vacuum tank.