A highly reliable magnetic recording/reproducing apparatus is provided. In the magnetic recording/reproducing apparatus, a spin-valve film is used as a magnetic sensor element for detecting magnetic signals. By defining the corrosion potential of this spin-valve film, and further by specifying the residual magnetization of a magnetic recording medium used as well as the product of the residual magnetization and the thickness of the magnetic layer to a range that is numerically optimal, the occurrence of corrosion on the surface of a magnetoresistive head that contacts the medium is prevented, and the occurrence of electromagnetic discharge is avoided. Further, by numerically specifying the surface resistivity of the metal magnetic thin film of the magnetic recording medium, as well as the roughness of the surface on which the metal magnetic thin film is formed, electrostatic discharge preventing effects and wear resistance are improved.