A computer system comprises two or more computers including at least one standby computer and a management computer which controls the computers. The management computer manages unique identification information which is assigned to an Ethernet controller of each computer. When a failure has occurred to an active computer, the management computer sets the unique identification information which has been assigned to the Ethernet controller of the failed computer to the Ethernet controller of the standby computer and the standby computer boots up a software image for the failed computer by use of the unique identification information which has been set to its Ethernet controller by the management computer.