Abstract: Axially extending liquid-tight tapered spaces are defined in the barrel of a roll body. Tapered pistons are fitted in the spaces for engagement and disengagement with a bore inner surface defining the tapered spaces. A liquid under pressure is supplied through liquid passages to some of liquid pressure chambers at opposite ends of the tapered pistons so that the barrel of the roll body is increased or decreased in diameter. When the rolling forces are removed from the roll body, the roll body returns to its initial straight state.

Abstract: Each of a pair of opposing slides which is equipped with a die and is connected through a connecting rod to an eccentric portion of a crankshaft is displaced by a width setting device in the direction of width of a slab so as to set the width of a slab to be forged between the pair of dies. After the setting of the width of a slab to be forged, the crankshaft is rotated to cause each of the slider-pair to reciprocate not only in the direction of width of the slab but also in the direction in parallel with the slab transportation line, whereby a slab is forged.