Abstract: To improve communication efficiency during the updating of a replica, and to reduce the amount of memory required for the updating of a replica. The present invention is a computer for maintaining consistency of replica contents by interchanging data modification with another computer. The computer includes: a replica including shared data; a receiver for receiving, from another computer, a modification request for data included in the replica; and a controller for controlling, regardless of a receiving order of the modification request, for each receipt of the modification request, a timing of update execution for the replica in accordance with the received modification request by using information included in the modification request. The timing of replica updating in accordance with the received modification requests can be determined, regardless of the order in which the modification requests are received, that is, the order of the transmission from other computers.