PURPOSE: To prevent undesired electric discharge between a magnetic head and a magnetic disk medium and to protect a power source and a circuit from being damaged.

CONSTITUTION: In the magnetic head 2, a coil 24 is wound around core 23, and both ends of the coil 24 are connected to head terminals 21, 22. By respectively connecting these head terminals 21, 22 to magnetic head connection terminals 31, 32 of a preamplifier 3, the magnetic head 2 is connected electrically to the preamplifier 3. The preamplifier 3 whose power source terminal 34 is +5V is connected to a positive voltage output terminal 41 of a DC-DC converter 4, and, ground terminal 35 is connected to the negative voltage output terminal 42, and is operated by a positive voltage and a negative voltage generated by the DC-DC converter 4.