A magnetoresistive effect element includes a recording layer having magnetic anisotropy and a variable magnetization direction, a reference layer having magnetic anisotropy and an invariable magnetization direction, an intermediate layer between the recording layer and the reference layer, an underlayer containing scandium (Sc) and disposed on a surface side of the recording layer opposite to a surface side on which the recording layer is disposed, and a side wall layer containing an oxide of Sc and disposed on side surfaces of the recording layer and the intermediate layer.