In this study, we investigate the backup-system using peer-to-peer network system. In general, as a way to backup the data, we use magnetic tape, hard-disk, flash memory, file server, and online storage, etc. However, these devices have some problems on redundancy, dispersiveness, or security. We propose fault tolerant data backup system with peer-to-peer network. To improve the level of redundancy and dispersiveness, our system employs the number of peer-to-peer network's nodes and redundant encrypting backup data. We attempt to reduce the nodes' load by halving backup data and sending it to separate nodes.