PURPOSE: To improve the stability for drive of a tape by varying intrinsic characteristics of a tension arm device by controlling a damping device for revolution of the tension arm device.

CONSTITUTION: A tension arm 17 is turned from its position within a range shown by a tension arm 17' by the tension of a magnetic tape 1. At the same time, a piston 27 is also shifted to a position shown by a piston 27'. In response to the shift of the piston 27, the gas within a damping mechanism 18 is circulated via a pipe 31 and a damping mechanism control part 19. In this case, a control signal is applied to an input terminal 33 so that the part 19 disturbs the circulation of gas. Thus the movement of the arm 17 becomes heavy. While the movement of the arm 17 is lightened if the control signal is applied so as not to disturb the circulation of gas. Thus a phenomenon, e.g., the tape resonance, etc. which is due to the intrinsic characteristics of a tension arm device is prevented. Then the stability is improved for drive of the tape 1.