An authentication processing system includes a communication network, a plurality of terminal apparatuses, and an authentication undertaking apparatus. The authentication undertaking apparatus authenticates the user of each terminal apparatus through utilization of data which include at least either data fixedly assigned to the terminal apparatus or data peculiar to the user, specifies a site which the user wishes to utilize, and undertakes authentication processing with reference to a database which stores authentication data which become necessary when the authenticated user utilizes the desired site.