Virtual machine configuration information and physical machine IDs are collected from physical machines in association with each other. In addition, among information stored in a management table which stores them, a physical machine ID corresponding to the collected virtual machine configuration information, and it is determined whether or not the detected physical machine ID matches with the collected physical machine ID. Herein, in a case of determining not-matching, a physical machine of a source of the collected information is requested to change the virtual machine configuration information.