Summary form only given. Recently, there has been increasing interest in research of data sharing in peer-to-peer networks. In this paper, we propose a new update propagation strategy that achieves not only load balancing but also delay reduction, where the update information is immediately notified to all peers holding the replicas when the update occurs. The proposed strategy creates an n-ary tree whose root is the owner of the original data and the other nodes are peers holding its replicas, and propagates the update information according to the trees. Moreover, we verify the effectiveness of the proposed strategy by simulation experiments.