FIG. 1 shows an example of the functioning layer 4 wherein a metal film 6 made of Ag or Au or the like is sandwiched between dielectric films 5, 7 which include a material such as ZnO, SnO2, ITO or the like as the major component to thereby form a multi-layered film, and a controlling layer 8 is formed at the bonding surface of a plastic layer 3 as an interlayer.