PURPOSE: To prevent recorded information from being erased by an external magnetic field by providing superconductors to cover both faces of a magnetic medium and rebounding the magnetic flux of the external magnetic field by the superconductors.

CONSTITUTION: The front and rear faces of a magnetic film 12 with which writing and reading-out of information are carried out are covered by the superconductors 14, 16. The superconductors 14, 16 are formed of a yttrium oxide and become superconducting in liquid nitrogen. A magnetic card 10 constituted in such a manner exhibits a superconducting state when the superconductors 14, 16 are preserved in liquid nitrogen. The magnetic flux is, therefore, rebounded by the superconductors 14, 16 by the Meissner effect thereof and is prevented from intruding into the conductors 14, 16 even if the external magnetic field exists around the magnetic card. Since the external magnetic field does not act on the magnetic medium 12, the erasing or changing of the information recorded on the medium 12 is prevented.