To set the optimum initial bias at the time of starting a motor by making the influence from the outside reflect to the initial bias.

In a controller 2 for bias group, the initial biases are computed for every detection result outputted from detector group 3, and all of the obtained initial biases are added, and based on these initial biases, the initial biases corresponding to the tape speed are calculated individually for the tape running speed as the initial biases. Next, the initial value BSet1 of the calculated bias for the tape running speed is stored in a bias initial value storing part 6 for the tape running speed. Further, the initial value Bcopy of the bias stored in the bias initial value storing part 6 is stored in a bias storage part 5 in accordance with the tape running speed at the time of starting the motor. Finally, the output signal Ct1 from a controller 1 for motor group and the output Badd of the bias storage part 5 are added by an adder 4, then the resulting sum Vm is outputted to the motor 7.