(1) A configuration management in a management server is carried out such that setting patterns regarding creation of plural types of virtual resources and setting patterns regarding connection between the plural types of virtual resources are extracted from setting information of network devices configuring a virtual network by using plural types of virtualization technologies, (2) an ID required for creating a virtual resource and a connection relation between virtual resources are extracted from the extracted setting pattern, (3) an element corresponding to a virtual resource or a connection between a pair of virtual resources is created by using information including the extracted ID, and (4) the elements created from setting information of individual devices are aggregated to thereby create logical topology information representing a topology of the virtual network.