A magnetoresistive effect element according to one aspect of the present disclosure includes a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer. The spacer layer is provided between the first ferromagnetic layer and the second ferromagnetic layer. The spacer layer includes an Mn alloy represented by General Formula (1). MnγX1-γ  (1) (in the Formula, X is at least one metal selected from the group consisting of Al, V, Cr, Cu, Zn, Ag, Au, an NiAl alloy, an AgMg alloy, and an AgZn alloy, and γ is 0