Abstract: There is provided a method of protecting confidential files to securely protect business confidential files in accordance with a security policy. In the method of protecting confidential files according to the present invention, information of a business application which is allowed to access confidential files is registered in a management server in advance and the registered application information is distributed to each client as needed. When the business application references confidential files, it is judged (application is authenticated) at the time of starting up the business application whether the business application is the application registered in advance in the server. Only when the application authentication is allowed, process information of the business application is registered in an I/O acquisition module. The I/O acquisition module allows only the process which is consistent with the registered process information to access confidential information, and rejects other processes.