PURPOSE: To shorten changing work time of a mold by using a changing carriage.

CONSTITUTION: At the time of changing the mold 22 by using the mold changing carriages 7A, 7B shiftable in the interval between a casting position and a waiting position, mounting the mold 22 and a supporting device for cast slab just below the mold, before changing, a head side dummy bar 31a composed of a head 32 and a head side drawing link 33a is fitted to the mold 22 and the supporting device for cast slab just below the mold newly fitted and also gap between the mold 22 and the head 32 is sealed and the changing carriage 7A for the mold after using is carried out from the casting position. Thereafter, a rail side dummy bar 31b composed of a tail side drawing link 33b is fitted between pinch rollers 5, and after the mold changing carriage 7B mounting the new mold 22 and the supporting device for cast slab just below the mold is shifted to the casting position X, the head side dummy bar 31a and the tail side dummy bar 31b are connected through a connecting part 34.