Even when a large number of guest OSs exist, a failover method meeting high availability needed by the guest OSs is provided for the each guest OS. In the event of a physical or logical change of a system, or change of operation states, a smooth failover method can be realized by preventing the consumption of resource amounts due to excessive failover methods, and the occurrence of systemdown due to an inadequate failover method. In a server virtualization environment, in a cluster configuration having a failover method due to hot standby and cold standby, by selecting a failover method meeting high availability requirements specifying performance during failover of applications on the guest OSs, a suitable cluster configuration is realized. Failure monitoring is realized by quantitative heartbeat.