Stable writing is performed in a super high density hard disk where writing by magnetic field is difficult. A layered thin film structure including at least a magnetic metallic layer/a non-magnetic metallic layer/a magnetic metallic layer is formed, and a metallic probe is brought close to this multilayer film on the order of nano-meters. A quantum well state created in the multilayer film is changed by applying a voltage between the metallic probe and the multilayer film, resulting in a relative magnetic field between the magnetic metallic layers being changed. At this time, an assistance magnetic field is applied in the writing magnetization direction.