An MR element comprises: a tunnel barrier layer having two surfaces facing toward opposite directions; a free layer disposed adjacent to one of the surfaces of the tunnel barrier layer and having a direction of magnetization that changes in response to a signal magnetic field; and a pinned layer disposed adjacent to the other of the surfaces of the tunnel barrier layer and having a fixed direction of magnetization. The tunnel barrier layer is made of a material containing an oxide semiconductor such as ZnO. The MR element has a resistance-area product that falls within a range of 0.3 to 2.0 .OMEGA.-.mu.m.sup.2 inclusive.