A memory function body has a medium interposed between a first conductor (e.g., a conductive substrate) and a second conductor (e.g., an electrode) and consisting of a first material (e.g., silicon oxide or silicon nitride). The medium contains particles. Each particle is covered with a second material (e.g., silver oxide) and formed of a third material (e.g., silver). The second material functions as a barrier against passage of electric charges, and the third material has a function of retaining electric charges. The third material is introduced into the medium by, for example, a negative ion implantation method.