In a high available clustered computer system, a standby computer starts up takeover preparation procedures at a time when occurrence of a failure is watched in an active computer and failover procedures will be started up from the takeover preparation completion status when the failure is detected in the active computer. Thus, speeding up of failover preparation procedures is realized.With such arrangement, it is possible to realize failover procedures by the hot-standby procedures when a failure occurs in an active computer.