PURPOSE: To roll a pipe under high rolling reduction by an installation of small capacity and to press-reduce the pipe in high dimensional accuracy by moving ring rolls in the direction intersecting with a mandrel axis to reduce the wall thickness of pipe.

CONSTITUTION: Ring rolls 3, 4, 5 are arranged in a row to form a caliber row. A cylindrical pipe 7 in which a cylindrical mandrel 6 is inserted, is advanced in this caliber row in the direction of pipe axis. Next, one or more of the rolls 3, 4, 5 are moved in the direction intersecting with the mandrel axis 8, to press-reduce the wall thickness of pipe 7. Further, the vibrations of mandrel 6 are restrained by holding the parts of mandrel 6 exposed from the pipe 7 by bar supporters 21, 23. The center of axis 8 is displaced across a mill center line and reversely to the direction to which the mandrel 6 tends to displace.