A pinned magnetic layer 20 and a free magnetic layer 26 include a magnetic portion 17 and a magnetic sublayer 22, respectively, each comprising a half-metallic ferromagnetic alloy. Since each of the magnetic portion 17 and magnetic sublayer 22 comprising the half-metallic alloy layer has a larger value .beta. and a larger resistivity .rho. compared to the conventional CoFe alloy or the like, the change in resistance (.DELTA.R) can be increased, and the rate of change in resistance (.DELTA.R/R) can be appropriately improved.