PURPOSE: To shorten working time for changing a precedingly used nozzle to a change-over nozzle by setting a pipe for the change-over nozzle at the position sufficiently apart from the precedingly used nozzle and extending tip part of the pipe to the prescribed position.

CONSTITUTION: The pipe 28 used to the change-over nozzle 26 is set in the refining layer 16 apart from the precedingly used nozzle 24 arranged at the bottom part of a converter 10. Then, the refractory layers 14, 16 around the above nozzle 24 are selectively eroded, and the above pipe 28 is set so as to expose the tip part thereof, when the exposed surface in the furnace near the above nozzle 26 retreats to the line 22. At this time, surrounding of the above nozzle 24 reaches thickness of the permanent brick layer 14.