A magnetoresistive head in which Barkhausen noise is substantially suppressed and a variation in reproduction is minimized, and a magnetic disk apparatus using the same magnetic head have been provided. The feature of the magnetic head and the magnetic disk apparatus of the invention resides in the provision of a longitudinal bias layer which comprises a hard magnetic thin film formed on an underlayer made of either a ferromagnetic thin film having a body-centered cubic lattice crystal structure, or an amorphous ferromagnetic thin film or antiferromagnetic thin film having a body-centered cubic lattice crystal structure.