A submerged nozzle supporting-replacing mechanism, which is constituted to set an entire width dimension (L3) of each of clampers (20 and 21) to be smaller than a flange diameter dimension (L1) of a submerged nozzle (9) so as to position each of the clampers (20 and 21) by a positioning member (26), and so as to guide an upper surface (43) of a fresh submerged nozzle (9A) by a positioning liner (6), to thereby regulate a height position of the fresh submerged nozzle (9A) during movement in a horizontal direction thereof. The position of the clampers are regulated by setting the entire width dimension of the clampers to be smaller than the flange diameter dimension of the submerged nozzle, which can be smoothly replaced by providing the positioning liner.