To prevent noise, vibration and dust generated by a follower roll driving mechanism and to prolong the service life of a gear, a universal joint or bearings by separating the engagement between gears of a follower roll side and a helper motor side when rotational peripheral speeds of the follower roll and a main driving roll are synchronized.

After a starting, in a state in which rotational speeds of respective rolls including a top roll 421 and a main driving roll, that is, the bottom roll arranged at the last stage of follower rolls are synchronized, a roll side gear 12 is separated from a follower side roll in which the nipping of a magnetic tape is completed by successively breaking off a clutch 63, stopping a helper motor 5 and pushing the rotary shaft 62 of a motor side gear 61 with a gear separating device 7. Thus, in a surface treating device, a roll side gear 4212, a universal joint 65 and the helper motor 5 are stopped during the high speed operation of the device and noise, vibration and dust generated by the follower roll driving mechanism are prevented.