PURPOSE: To aim polishing a VTR head under the application of uniform tape tension, by providing a feed means for a means for ditecting the tension of a polishing tape and a means for setting the tension which is a detected value so that it is possible to cope with variations in the diameter of the wound tape and variations in load.

CONSTITUTION: The tension of a polishing tape 1 is detected such that the strain of a leaf spring 13 is converted into an electrical signal by a strain gage 12 applied on the leaf spring 13 and a tension amplifier 16. Further, a comparator 17 compensates an error from a set tension 18, and effects hysteresis brake for applying back tension to a supply reel 2 by means of a clutch brake 15, through an error amplifier and a driver 20. Thus, variations in tape tension due to changes in the diameter of the wound tape and due to variations in load may be detected and therefore, the brake is exerted to make the tape tension always equal to the set tape tension, thereby it is possible to polish heads 7, 7' under uniform tape tension.