In a presence system in which one user users a plurality of terminals, dynamically changing buddy lists are synchronized between the terminals. A presence notification message is sent to all the terminals of the user. The timing of sending includes, for example, when the presence information of a buddy is updated, when a new buddy is set, when display attribute information is updated, when a buddy is cancelled, and when a presence notification of unknown presentity is made. Thus, when one user uses a plurality of terminals in the presence system, dynamically changing buddy lists can be synchronized between the terminals. In addition, the display formats of the buddy lists do not differ from one terminal to another, and the same display format is attained.