A magnetometric sensor comprising: a magnetoresistance effect element (11, 11') having a sensitivity axis in a specific direction, wherein the magnetoresistance effect element (11, 11') has a layered structure on a substrate, the layered structure comprising a fixed magnetic layer and a free magnetic layer (23, 33) stacked with a nonmagnetic material layer interposed therebetween; the magnetoresistance effect element (11, 11') includes a first antiferromagnetic layer on the free magnetic layer (23, 33) on the opposite side to the side facing the nonmagnetic material layer to cause an exchange coupling bias between the first antiferromagnetic layer and the free magnetic layer (23, 33) to make the magnetization direction of the free magnetic layer (23, 33) in a prescribed direction in a state of permitting variation in magnetization; characterized in that the free magnetic layer includes: a misfit-reducing sub-layer for decreasing the lattice mismatch of the free magnetic layer with the first antiferromagnetic layer; a misfit-reducing sub-layer being in contact with the first antiferromagnetic layer and decreasing the lattice mismatch of the free magnetic layer with the first antiferromagnetic layer; and a ferromagnetic sub-layer made of a ferromagnetic material disposed on the misfit-reducing sub-layer on the opposite side to the side facing the first antiferromagnetic layer. a magnetoresistance effect element (11, 11') having a sensitivity axis in a specific direction, wherein the magnetoresistance effect element (11, 11') has a layered structure on a substrate, the layered structure comprising a fixed magnetic layer and a free magnetic layer (23, 33) stacked with a nonmagnetic material layer interposed therebetween; the magnetoresistance effect element (11, 11') includes a first antiferromagnetic layer on the free magnetic layer (23, 33) on the opposite side to the side facing the nonmagnetic material layer to cause an exchange coupling bias between the first antiferromagnetic layer and the free magnetic layer (23, 33) to make the magnetization direction of the free magnetic layer (23, 33) in a prescribed direction in a state of permitting variation in magnetization; characterized in that the free magnetic layer includes: a misfit-reducing sub-layer for decreasing the lattice mismatch of the free magnetic layer with the first antiferromagnetic layer; a misfit-reducing sub-layer being in contact with the first antiferromagnetic layer and decreasing the lattice mismatch of the free magnetic layer with the first antiferromagnetic layer; and a ferromagnetic sub-layer made of a ferromagnetic material disposed on the misfit-reducing sub-layer on the opposite side to the side facing the first antiferromagnetic layer. a misfit-reducing sub-layer for decreasing the lattice mismatch of the free magnetic layer with the first antiferromagnetic layer; a misfit-reducing sub-layer being in contact with the first antiferromagnetic layer and decreasing the lattice mismatch of the free magnetic layer with the first antiferromagnetic layer; and a ferromagnetic sub-layer made of a ferromagnetic material disposed on the misfit-reducing sub-layer on the opposite side to the side facing the first antiferromagnetic layer.