The present disclosure provides an authenticity verifying system capable of generating renewed database and updating unlock number upon occurrence of information leak, and comprises product (1) having lock device (11) with infrared ray transceiving unit (12) and keypad (14), and scratch card (13) with password and product serial number provided thereon; a manufacturer's verifying server (2) for verifying product authenticity through a commercial communication network; and an unlock number change device (3) responsive to leak of information stored in server (2) for downloading, from server (2), predetermined password that matches product (1) and renewed unlock number newly matched to the product serial number. Further, the present disclosure provides a method for verifying product authenticity through acquiring an unlock number, and comprises performing an unlock number acquiring process and applying the unlock number acquired to lock device (11) of product (1) to unlock lock device (11).