Abstract: A magnetic tape apparatus (1) comprises a drive mechanism for driving a magnetic tape (7) and reels (5, 6), a magnetic-head mechanism (9, 10), a buffer mechanism a belt (8) and guide elements (21, 22, 23, 24), which guide the belt (8) in the operational position, which apparatus (1) also comprises a control system for controlling the tape tension, for controlling the position of the belt (8) in the operational phase and for locating a desired part of the tape. The control system comprises a position detection mechanism (38) a tape-tension detection mechanism (44), and a control unit (45) for controlling the reel and tape drive mechanism.