When the status of a client X is changed to a status i, a group management unit generates a group agent Xi, corresponding to the status i and registers the generated group agent in the server S, and the presence issuing unit issues the status i and the identifier of the group agent Xi. Initially, a member management unit of the group agent xi manages the client X only. When other clients, such as clients B and C, that are observing the status of the client X send an instant message (IM) to the group agent Xi identified by the issued identifier, an IM delivery unit of the group agent Xi adds the clients B and C, which are IM senders, to the members managed by the member management unit and sends the IM to all members.