There is provided a method of adding a new computer as a standby computer to a computer system that includes an active computer for performing service processing and a standby computer for storing replica of data stored in the active computer. The replica of the data stored in the standby computer is updated when the data stored in the active computer is updated. The method comprising the steps of: selecting the standby computer from the computer system; transferring the replica of the data stored in the selected standby computer to the new computer; and transferring update information on data updated in the active computer after the transferring the replica of the data is started, to the new computer.