A network service user authentication system is provided to properly authenticate an authorized user in a transaction using a network. The system includes an includes an authentication part which preserves vital information for confirming a user and issues authentication information on the user by collating vital information supplied from outside through a network with the preserved vital information, and a payment part of a financial institution which, upon receiving the authentication information on the user issued by the authentication part, performs the payment admission of an amount to be paid to a provider server which provides a commodity or a service to the user through the network.