PURPOSE: To prevent a structure having the same area and shape as an authentication structure from being formed from a used forgery prevention sheet, by a method in which, in the case a section whose area and shape are substantially the same as those of a formation predetermined section is specified from a non-formation predetermined section, the structure of the specified non-formation predetermined section is made different from the structure of the formation predetermined section.
CONSTITUTION: In a part corresponding to the formation predetermined section 12 of an authentication structure formation layer 14, a mosaic-like relief- diffraction-grating with lines in different directions or at different intervals is formed as an authentication structure. In a non-formation predetermined section 13, a light-scattering structure obtained by a mat processing, etc., is formed; however, the reflecting layer 15 of the part 19 corresponding to the letters 'VOID' is removed. In the relief of the part from which the reflecting layer 15 is removed, a bonding layer 16 made of a material having the same refractive power as the material of the authentication structure formation layer 14 is embedded. Because it is very difficult to remove the bonding layer 16 and reproduce the relief, this is very useful to prevent forgery.
DANJO KOTARO
TAWARA SHIGEHIKO
