A bias circuit for a magneto-resistive head having a bias current output circuit
for flowing a bias current through a magneto-resistive head, and a feedback circuit
for controlling the bias current from a bias current output circuit by detecting
voltage variation across the magneto-resistive head so that a voltage across the
magneto-resistive head becomes a predetermined value. The bias current output circuit
comprises a regulating circuit for regulating an operation of the bias current
output circuit in the bias current output circuit, a control circuit for controlling
the regulating circuit to be in a predetermined condition, and a switching circuit
for switching a read/write condition for activating the control circuit for the
regulating circuit in a non-read condition of the magneto-resistive head. The regulating
circuit includes an oscillation suppressing capacitor; and the control circuit
for the regulating circuit is a charging circuit for the oscillation suppressing capacitor.