PURPOSE: To enable to make the temp. of molten steel uniform while adjusting components, by specifying the relationships of the downward ejection angle of a bottomed dipping lance, a distance between the top end of an ejection opening and the bottom of a ladle and a distance between the ejection opening and the side wall of the ladle.

CONSTITUTION: A bottomed dipping lance 11 for injecting O2 into molten steel inside a ladle 15 has a plurality of downward ejection openings 14 engraved with a predetermined angle θ (0<θ≤60°) directing downwards from the lower side surface and arranged in the same intervals along the circumferential direction. By said lance 11, the molten steel inside the ladle 15 is bubbled. Hereon, the bubbling is performed subject that a distance l between the openings 14 and the side wall of the ladle 15 and a distance H between the top ends of the openings 14 and the bottom of the ladle 15 satisfy Formula II or IV in case of Formula I or III, respectively.