The present invention provides a spin-valve magnetoresistance sensor in which are formed, on top of the substrate, free layers, and pinned layers, enclosing a nonmagnetic spacer layer, and an antiferromagnetic layer adjacent to the pinned layers. The sensor is also equipped with a back layer including at least two nonmagnetic metal layers adjacent to the free layers on the side of the free layers opposite the nonmagnetic spacer layer. The back layer has at least one nonmagnetic metal layer of Cu with high electrical conductivity, preferably formed adjacent to the free layers, as for example in a two-layer structure of Cu and Ru or a three-layer structure Ru/Cu/Ru. In addition to a high read output, fluctuations in Hint with the film thickness of the back layer can be suppressed and sensor characteristics stabilized, and high recording densities can be realized.