A repositioner for a streaming magnetic tape drive apparatus includes control circuitry which, when a repositioning instruction is received from an external device, supplies a drive stop instruction to a tape reel motor and a measurement start instruction to a tape travel distance measuring device when a first data block edge detection signal is reproduced from the tape within a certain time period. A tape stop detection signal is produced when forward movement of the tape ceases, and the control circuitry outputs a reverse drive instruction to the reel motor while supplying a reverse tape travel distance measurement start instruction to the distance measuring device. When the forward and reverse tape travel distances become equal and a data block edge detection signal is reproduced from the tape within a certain time period, a normal operation signal is provided to the external device to signal that a repositioning operation is normally performed. Accordingly, adjacent data blocks on the tape will not be erased, and data read access will not be started midway along an adjacent data block on the tape.