A data-management system manages identical data stored in main-memory areas of several computers connected via a network. The system has a transaction acceptor to accept a request for executing a transaction of accessing the database, a transaction executor to execute the transaction, a replication processor to process the replica data to reflect updated data sent from the original site and a data receiver and a data transmitter. An updating transaction for the data of the database is performed by the transaction executor but allowed only for the original site. The updated data is transmitted from the data transmitter of the original site and received by the data receiver of the replica site and reflected on the replica data of the replica site by the replication processing section.