PURPOSE: To prevent damage when abnormality is caused, and sharply reduce a quantity of compressed air to be used.

CONSTITUTION: A bearing of a separate roller 7 is composed of a dynamic pressure type air bearing part 1 in no need of compressed air at rotating time and an air bearing by a static pressure type air bearing part 2 in need of it, and supply of the compressed air is stopped at steady operation time, and a cylinder 4 is supported with the dynamic pressure type air bearing part 1, and a quantity of air to be used is set in O. When a detector detects electric continuity between these by generation of an overload by contact between the cylinder 4 and the air bearing, a solenoid valve is opened, and the compressed air is supplied to the static pressure type air bearing part 2, and the cylinder 4 is supported, and damage to the separate roller 7 is prevented.