A cart ID according to the present invention is an identification code including receipt information containing at least a receipt number (serial number) indicating a receipt number of the transaction, and further unmeaning password information. Furthermore, it is preferable that the receipt information has date information in which the cart ID is issued. In this manner, the cart ID according to the present invention contains the password information in addition to the receipt information having conventional date information and the receipt number, whereby even when the cart ID is disclosed to the principal, it is possible to prevent another person from being informed thereof.