A magnetoresistance effect element has a first ferromagnetic metal layer, a second ferromagnetic metal layer, and a tunnel barrier layer that is sandwiched between the first and second ferromagnetic metal layers, the tunnel barrier layer is expressed by a chemical formula of AB 2 O x , and has a spinel structure in which cations are arranged in a disordered manner, A represents a divalent cation that is either Mg or Zn, and B represents a trivalent cation that includes a plurality of elements selected from the group consisting of Al, Ga, and In.