A magnetoresistive element 11 is formed with inclusion of a free layer 12, a pinned layer 13, an antiferromagnetic layer 14 for pinning the pinned layer 13, an intermediate layer 15 provided between the free layer 12 and the pinned layer 13, and a ferromagnetic layer 16 for applying a longitudinal bias magnetic field to the free layer. After initial magnetization, characteristic evaluation is conducted for the magnetoresistive element 11. Intensity of longitudinal bias field is adjusted by magnetizing again in a direction different from that of the initial magnetization, if required, on the basis of the evaluation result.