PURPOSE: To prevent information from being leaked due to the direct reference of circular data in a storage area or the aquisition of circular data by a person posing as a normal referencer in the case of requiring the secrecy of the circular data and to enable only a normal referencer to receive information.

CONSTITUTION: When an inputted user password 10 is judged as a correct one, how to refer to circular data in a distributed destination 7-1 is determined. If an incorrect user password 10 is inputted and its invalidity is judged, its trial frequency is checked. When a user tries to refer to circular data illegally as a distributed user 7-2 inputs an invalid user password 10 by the determined number of times, the existence of an invalid referencer in a distributed destination 7-2 is informed to a transmitter 3 by means of mail or direct sending of a signal to a terminal.