MAGNETIC DISK DEVICE

PURPOSE:To minimize the amount of the asymmetry of upper/lower and the peak shift amount of a reading waveform by optimally adjusting a bias current value through a magneto-resistance effect head for the whole recording areas of a magnetic disk medium. CONSTITUTION:The reading waveform with a fixed frequency is sent to an upper/lower asymmetry detection part 10 through a read amplifier 8, and an upper/lower asymmetry amount of DELTAV is generated in the part 10 to be sent to an A/D converter 12. Further, a data pulse with a minute pulse width according to the peak position of the reading waveform is generated by a pulse forming circuit 9, and the pulse is sent to a signal distinguishing circuit 14 and a peak shift detection part 11. The peak shift amount of DELTAT is generated in the detection part 11, and the amount DELTAT is sent to the converter 12. A signal 21 according to the amounts of DELTAV, DELTAT is generated in the converter 12 to be sent to a control signal generator 13. A current control signal 22 is generated according to a control signal 19 based on the signal 21 by the generator 13.