PURPOSE: To suppress deformation of a Ni-P substrate and to obtain stable low-height floating traveling of a magnetic head by specifying the difference of film thickness between Ni-P alloy layer formed on the both sides of a nonmagnetic substrate.

CONSTITUTION: On the both sides of a disk-type A1 alloy plate 11, Ni-P alloy layer 12, magnetic layer 3 and protective layer 4 are formed. The difference of film thickness between the Ni-P alloy layer 12 formed on one side of the substrate and the other Ni-P alloy layer 12 on the other side is specified to <0.035 % of the thickness of the Al alloy plate 11. Namely, variation in the flatness of the disk is caused by the difference of film thickness of Ni-P alloy layers each formed on the one side (side A) and on the other side (side B) of the Al plate 11. Thereby, by specifying the difference of film thickness, flatness of the disk can be improved.