A history information storage unit accumulates an interaction history which corresponds to
each interaction session performed by a communication terminal and which at least contains
the other-party user ID and the other-party terminal ID. If User A, who is interacting with the
terminal b1 of User B, sends from the terminal 1 a an interaction history request containing
the ID of User B and the IDs of the other terminals a2 to an owned by User A, a history
information computation unit searches, from the history information storage unit, the …