PURPOSE: To support the outside diameter of a hollow shell by fastening support rolls to an interval where the hollow shell is not pressed and not held after the end part of hollow shell is passed through the support rolls.

CONSTITUTION: A mandrel 25 is held in between using cylinders 13, 14 in a support device until the side end part of the hollow shell 16 approaches a top roll 1 and bottom rolls 2, 3 for support. Just before the side end part of the hollow shell 16 is passed through the support rolls 1, 2, 3 of the support device, intervals between the support rolls 1, 2, 3 are opened to the intervals where the side end part of the hollow shell 16 does not collide. After the side end part of the hollow shell 16 is passed through the support rolls 1, 2, 3, the support rolls 1, 2, 3 are fastened to the intervals where the hollow shell 16 is not supported and not held in between and the vibration of the shell in rolling is suppressed. In this way, pressing and holding in between the hollow shell are eliminated.