A magnetoresistance effect (MR) device incorporating a spin valve film, and a magnetic head, a magnetic head assembly and a magnetic recording/reproducing system incorporating the MR device, wherein the magnetization direction of a free layer is at a certain angle to the magnetization direction of a second ferromagnetic layer therein when the applied magnetic field is zero. A pinned magnetic layer includes a pair of ferromagnetic films antiferromagnetically coupled to each other via a coupling film existing therebetween. The magnetization direction of either one of the pair of ferromagnetic films constituting the pinned magnetic layer is maintained, and a nonmagnetic high-conductivity layer is disposed adjacent to a first ferromagnetic layer on the side opposite to the side on which the first ferromagnetic layer is contacted with a nonmagnetic spacer layer. With that constitution, the device has extremely high sensitivity, and the bias point in the device is well controlled.