In an update management system including a plurality of servers executing a communication service, a server (VNF2) not connected to a network in which a new version of an application is operated is generated in parallel with a server (VNFM1) in which an old version of the application is operated, and old and new correspondence data between an old version server and a new version server is generated and used to execute switching from the old version server (VNF1) to the new version server (VNF2) in a flow on the network and to execute switching-back to the old version server (VNF1) by referring to the old and new correspondence data at the time of occurrence of fault in a new version.