A load balance server has a first database for recording a list of identifiers of the presence servers, a second database for recording a subscription message receiving rate, an entry retrieval means for selecting a presence server that the subscription message receiving rate is lowest, in presence servers included in the list of the entry based on the presence information, a presence server selecting means for selecting an additional presence server whichever subscription message receiving rate is lower than predetermined threshold Ts, when the subscription message receiving rate in the selected presence server is higher than predetermined threshold Ts, and a message sending/receiving control means for sending the public message to the selected presence server.