PURPOSE: To prevent the occurrence and adhesion of scratches and foreign substances on a metal belt and a roll surface as well as to aim at improving the quality and economical efficiency of a device, by installing plural permeant holes in an outer cylinder of a support roll that supports the traveling metal band, while spouting air through an air turbine blade inside the cylinder.

CONSTITUTION: Compressed air is led into a base body 5 of a cylinder part via compressed air supply pipes 13aW13c, rotary couplings 12a, 12b, and air changing passages 10a, 10b, and spouted outside the base body 5 from permeant holes 7 as rotating an air turbine blade 11, namely, a support roll 3 being secured tight to the inner circumferential wall of the base body 5. In addition, centering on the permeant hole 7-1, the upward resultant force of the compressed air spouted out of plural permeant holes being opened within a range at some angles and in both directions, for example, 7-1, 7-2, 7-3, 7-4 and 7-2', 7-3', 7-4', works in a reverse direction to a compound belt consisting of gravity of a metal belt 1 and gravity of a plied paper belt 2, so that it enjoys a function to reduce the contact pressure that the metal belt 1 and the plied paper belt 2 both affect the surface of a support roll 3.