A magnetic storage device includes a magnetoresistive effect element. The magnetoresistive effect element includes a first ferromagnetic layer; a second ferromagnetic layer; a non-magnetic layer between the first ferromagnetic layer and the second ferromagnetic layer; and a first layer provided at a side of the first ferromagnetic layer opposite to a side of the first ferromagnetic layer at which the non-magnetic layer is provided. The first layer includes a rare-earth element and the first layer has a region including boron (B) at a proportion higher than a proportion of boron (B) in the first ferromagnetic layer.