To provide a secret information file protection system for an existing application by which it is possible to prevent the temporarily stored secret information from leaking to the third party by confining it inside a file even though a user can execute addition editing work by taking out a secret information file prepared by the existing application to the outside of an organization.

The user terminal is provided with a means for executing user authentication by transmitting a utilization request for secret data stored in a storage means of the user terminal to an authentication server, a means for receiving a common key for encoding/decoding the secret data according to the authentication result, a means for allowing the secret data to be edited with the existing application by decoding the secret data with the received common key for decoding, and a means for storing the secret data after the editing in the storage means by encoding the secret data after the editing with the common key for encoding.