In order appropriately to prevent leakage of an authentication symbol string such as a credit card number, and for it to be possible for a user to be authenticated as a legitimate user: an ID issuance server 20 receives the first eight digits of the credit card number from a portable telephone device 10 of the user and issues a one-time ID to the portable telephone device 10; a service provision server 30 receives the last eight digits of the credit card number and the one-time ID from a PC 11, and transmits the one-time ID and those last eight digits to a number construction and authentication processing server 40; and the number construction and authentication processing server 40 receives the one-time ID and the last eight digits from the service provision server 30, communicates with the ID issuance server 20 and acquires the first eight digits which correspond to the one-time ID, reconstructs the credit card number, and performs authentication with the credit card number.