A magnetic circuit is provided in an enclosure that can efficiently generate
magnetic
flux from the enclosure, configuring a magnetic disk, to a magnetic disk. Thus,
by providing such a magnetic circuit, a magnetic field different from that in other
enclosure parts, that is, a local magnetic field, is generated from the magnetic
circuit in case the disk device is set in an external magnetic field. Hence, this
local magnetic field can effectively erase data in the magnetic disk. In particular,
since the local magnetic field is generated even if the external magnetic field
is weak, it is possible to not only suppress the demagnetization of permanent magnets
used in the spindle motor at minimum, but also effectively erase data in the magnetic disk.
