Abstract: According to an aspect of an embodiment, a magnetic device comprises a head for writing data into or reading data from a medium, the head having an actuator for changing a flying height of the head over the medium, a storage for storing characteristic information of areas of the medium and a controller for controlling the actuator on the basis of the characteristic information of the areas of the medium when writing data into or reading data from the areas of the medium.

Abstract: A signal reproducing circuit for a magneto-resistive effect head includes a constant current source for supplying a sense current to an MR head in a read state, first constant current sources for supplying first constant currents to a pair of reproduction transistors in the read state, and a capacitor connected between the emitters of the transistors. Furthermore, second constant current sources for supplying second constant currents are connected in parallel with the first constant current sources. Control is given so that when switching an idle state to the read state is commanded, the second constant current sources remain on for a given period of time. Owing to this circuitry, a transient period during which the idle state is switched to the read state or a transient period during which heads are switched in the read state can be shortened to a great extent.