To provide a password automatic input substitution system reducing the labor of a user, and improving safety without generating the remarkable increase of cost.

When a user authentication request is issued from an application, an input and output monitoring device 11 starts a user identifying device 12, and allows this device to extract extraction information indicating the physical features of a user, and outputs it to a user collating device 13. The user collating device retrieves a user data base by using the inputted extraction information as a retrieval key, and outputs corresponding user ID and password to the input and output monitoring device. The input and output monitoring device supplies the user ID and password from the user collating device to the application.