An original authentication system and structural elements thereof is provided, in which it is possible to easily distinguish between an original and a copy. The checking device 13 comprises: a print sheet reading sensor 201 for reading the print pattern of the print sheet; a mark information checking portion 202 for detecting the mark information from the print pattern of the read print sheet, for checking the mark and for calculating the remaining mark amount; a generation control information detection portion 203 for detecting the generation control information of the print pattern of the read print sheet, and extracting the remaining mark amount from said generation control information; and a remaining mark amount comparison portion 204 for comparing the calculated remaining mark amount obtained by mark detection with the remaining mark amount extracted from the generation control information. A distinction can between deterioration in quality occurring when an original is printed out, and that occurring when subsequent copies are made, and thus it is possible to carry out authentication of a printed sheet as an original.