The utility model relates to a transmission device, in particular to a roller internally installed type iron caster, which provides the roller internally installed type iron caster of light overall weight of chain belt, advanced art structure, stable operation, convenient maintenance, long life-span and repeatable use of a fastening member for transmission device. The utility model comprises a plurality of cast iron molds of related joint in step shape and ear holders arranged on two sides of the cast iron mold, wherein, the cast iron mold is fixed on two chain belts by the ear holders. Each chain belt comprises a long shaft with a load wheel and a short shaft with a tension roller for connecting an outer chain plate and an inner chain plate alternatively. Two chain belts are connected movably by the long shaft and the short shaft to form a whole symmetrically. The ear holders arranged on two sides of the cast iron mold is positioned beneath the iron casting mould. Wing plates are arranged on the outer side of the outer plate of the outer chain plate and the outer plate of the inner chain plate. The ear holders are fixed with the wing plates. The structure can protect the chain belt and the fastening member from sputtering by the melted iron. No dragging wear exists between the load wheel and the rail, therefore, the maintenance and change of the iron casting mould are convenient. The screw can be used repeatedly with obvious economical benefit.