PURPOSE: To easily protect the file secrecy for each user by setting the names of groups of terminals as the elements to decide permission for use of the files.

CONSTITUTION: A session set-up means 4 acquires the information on each session via a terminal control means 2 and stores these acquired information into the session control information 5. When the terminal identification name and an acquiring request of the terminal group names are received from the means 4, a terminal control file control means 6 retrieves a terminal control file 7 and sends the terminal group name of the corresponding terminal identification name to the means 4 in reply. Then the means 6 compares the use-permitted terminal group name with the terminal group name informed from a conversation control means 3 against a file access request of the means 3 and decides whether the use of the relevant terminal is permitted or not. If not, the file access request is rejected. As a result, the secrecy can be easily protected for each group of user files.