A communication device has a configuration including a data analysis unit 1, a communication monitoring unit 2, and a management information transmission unit 3. The data analysis unit 1 extracts predetermined information from each of a plurality of packets input to the own device, analyzes the predetermined information of the plurality of packets, and generates information relating to a characteristic of each flow of the packets, as flow management information. The communication monitoring unit 2 detects that an abnormality occurs in communication of packets in a communication network to which the own device is connected. When the abnormality detection unit 2 detects the abnormality, the management information transmission unit 3 transmits predetermined information already extracted from a predetermined packet input before the detection of the abnormality, as information for generating the flow management information expected to be generated by the own device, to a standby-system device.