Restoration of all virtual machines are managed in respect of each restoration time thereof in a case where virtual machines at certain time in the past are restored under a server virtualization environment in which a plurality of virtual machines are constituted. A host computer creates a first snapshot of a first virtual machine at a first time specified by a management computer, and stores the first snapshot in a first logical volume of a storage device. Next, the storage system replicates in a second logical volume the first logical volume. In a case where the host computer creates a second snapshot of a second virtual machine at a second time that is before the first time and stores the second snapshot in the first logical volume, the management computer manages or displays the second snapshot creation time and snapshot information in association with the first snapshot creation time and snapshot information, respectively.