A magnetoresistance effect device having a basic structure wherein a multi-layer film comprising a unit of magnetic layer/non-magnetic layer/magnetic layer/antiferromagnetic layer, or antiferromagnetic layer/magnetic layer/non-magnetic layer/magnetic layer is formed with a protective film on a surface of the magnetoresistance effect device employing one of a metal, oxide material, nitride material, a mixture of oxide and nitride material, a double-layer film of metal/oxide, a double-layer film of metal/nitride, or a double-layer film of metal/(mixture of oxide and nitride) of film thickness between 2 nm and 7 nm.