PURPOSE: To contrive the improvement in the reliability of the material for the magnetic core by polishing the surface of a magnetic alloy thin plate obtained by quenching it from molten state, laminating the thin plates to increase the sapce factor of the material to prevent the deterioration of various properties thereof, and increasing the adhering strength thereof.

CONSTITUTION: The matnetic alloy thin plate obtained by quenching it from molten state is polished on the surface to roughness of predetermined maximum value by aqueous emery paper and buffer polishings. This thin plate is molded to final shape of magnetic head core by superhard alloy punching dies, heat treated as predetermined in hydrogen atmosphere, and predetermined number of the cores thus formed are laminated through predetermined number of epoxy resin or the like to form a head core. When it is thus polished and laminated, it increases the space factor of the material for the magnetic core to prevent the deterioration of the various properties thereof so as to increase the effective input and output for the magnetic head and to contrive the reduction in size for equipments such as a transformer, magnet astrictive device or the like.