A method of checking sheets as to forgery thereof, the sheet being provided with an electronic circuit chip from which information can be read cut or written and having visible information. The method includes a step of encrypting the visible information of the sheet and storing the encrypted visible information in the electronic circuit chip, and a step of determining discriminatively the authenticity of the sheet by comparing the visible information of the sheet with the information stored in the electronic circuit chip.
This is a continuation application of U.S. Ser. No. 09/857,271, filed Nov. 27, 2001 now U.S. Pat. No. 6,659,353 which is a 371 of PCT/JP99/06798 filed Dec. 13, 1999.
