According to the invention, a managing server, using a snapshot-appended information table which stores management information for identifying snapshots of a virtual server, a setting change table which stores setting change information on the virtual server, and a policy table which stores policies to be met by the virtual server, acquires the setting change information from the setting change table, selects the setting change information items from the acquired setting change information matching policies stored in the policy table, acquires management information on the snapshots of the virtual server from the snapshot-appended information table, identifies a snapshot of the virtual server with reference to the acquired management information, changes the identified snapshot of the virtual server based on the selected setting change information items, and rolls back the virtual server according to the changed snapshot.