In the method for replacing an immersion nozzle while pushing out a used immersion nozzle by a new immersion nozzle, in order to minimize leakage of molten steel during the replacement, to enable the use of a shaped joint sealer in a joint interface, and to ensure high sealability, a concave portion is formed on the new immersion nozzle's upper plane so as to include a nozzle hole, and the shaped joint sealer is mounted in this concave portion. The immersion nozzle's upper plane is caused to slide while being pressed to the upper nozzle's lower plane.