To write information on the surface without deteriorating design appearance of an article and its packaging.

In this article to be managed, a code string showing own management information is written as an invisible watermark on it or the surface of the packaging material covering it. In such a constitution, the ground part is recognized by the naked eye, but the invisible watermark to be overlaid on it is not recognized by the naked eye. Therefore, even when the invisible watermark of a JAN (Japanese Article Number) code is overlaid on the part having the name, picture, quality assurance display, or the like of the article, the part is not obscure and the design appearance of the surface of the article or the like is not deteriorated.