A ferromagnetic double quantum well tunneling magnetoresistance device is disclosed that utilizes a two-dimensional electron (positive hole) system to obtain an infinitely great magnetoresistance ratio. Also disclosed are a sensitive magnetic sensor and a nonvolatile storage device derived from that device. In structural terms of the device, a first and a second quantum well layer of ferromagnetic material (4, 8) in each of which the quantum confinement for carriers is established in a two-dimensional electron (positive hole) state are each sandwiched between a pair of barrier layers of nonmagnetic material (2, 6, 10) through which the carriers can tunnel. The first and second quantum well layers (4, 8) have a difference in coercive force so that when an external magnetic field is applied thereto only one of them may be reversed in the direction of magnetization. As a result, if magnetizations of the two quantum wells are parallel to each other, tunneling is allowed to occur, and if they are antiparallel to each other, tunneling is inhibited. A infinitely great tunneling magnetoresistance ratio is thereby obtained.