Embodiments of the invention prevent a decrease in magnetization or demagnetization from occurring to recording magnetization regardless of a direction in which a stray field is applied. In one embodiment, an apparatus for data storage system comprises a head having a magnetic field shield in the vicinity of a main pole, and a cover of the device, using a constituent material with a magnetic field shielding effect, across the cover, or at part thereof. When a stray field in a direction perpendicular to a recording medium is applied, the effect of the magnetic field is alleviated by the magnetic field shield installed in the vicinity of the main pole. In such a case, it need only be sufficient to form the magnetic field shield in a shape optimum for removing the stray field in the perpendicular direction only. When a stray field in a direction horizontal in relation to the recording medium is applied, the magnetic field acting on the recording medium is removed by the cover of the device comprising a magnetic component.