An endless track continuous casting machine having a pair of upper and lower endless belts facing each other in a spaced apart relationship and travelling in a downwardly slanted direction which form the long side walls of a mold. Dam blocks continuously and closely disposed and pinched between both side edges of the pair of endless belts and each supported by a link forming part of an endless chain wound around sprockets disposed on each side of the pair of endless belts form the short side walls of the mold. The dam blocks are mounted on each of the links of the endless chain to be movable inwardly and outwardly, and they are guided by a guiding mechanism to a projecting position when entering the advancing path of the mold and are guided to a set back position when entering the returning route. This guiding mechanism is adjustable to change the projected position of each dam block while the endless chain is moving, thus enabling the width of a cast piece to be altered without stopping the casting work.