A communication device that functions as a backup device comprising: a plurality of computing devices (110,120); and a plurality of second functional units (112,122,123) corresponding to a plurality of first functional units (112,122,123) of another communication device, wherein at least some units of the plurality of the second functional units are implemented on one of the plurality of the computing devices of the own device, the other second functional units (122,123) are implemented on the other computing devices of the own device, the plurality of the second functional units (112,122,123) respectively includes: a monitoring unit configured to transmit a response request to a corresponding first functional unit (112,122,123) of the another communication device, and configured to determine whether or not a response to the response request has been received from the corresponding first functional unit (112,122,123) of the another communication device, and a switching request unit configured to transmit, to the another communication device, a transfer-destination switching request for transferring packets that are supposed to be processed by the corresponding first functional unit (112,122,123) of the another communication device to the own device if the response has not been received from the corresponding first functional unit (112,122,123), the plurality of second functional units (112, 122, 123) is configured to process, in the computing devices (110, 120) on which they are respectively implemented, the packets transferred by the another communication device if the response has not been received. a plurality of computing devices (110,120); and a plurality of second functional units (112,122,123) corresponding to a plurality of first functional units (112,122,123) of another communication device, wherein at least some units of the plurality of the second functional units are implemented on one of the plurality of the computing devices of the own device, the other second functional units (122,123) are implemented on the other computing devices of the own device, the plurality of the second functional units (112,122,123) respectively includes: a monitoring unit configured to transmit a response request to a corresponding first functional unit (112,122,123) of the another communication device, and configured to determine whether or not a response to the response request has been received from the corresponding first functional unit (112,122,123) of the another communication device, and a switching request unit configured to transmit, to the another communication device, a transfer-destination switching request for transferring packets that are supposed to be processed by the corresponding first functional unit (112,122,123) of the another communication device to the own device if the response has not been received from the corresponding first functional unit (112,122,123), the plurality of second functional units (112, 122, 123) is configured to process, in the computing devices (110, 120) on which they are respectively implemented, the packets transferred by the another communication device if the response has not been received. a monitoring unit configured to transmit a response request to a corresponding first functional unit (112,122,123) of the another communication device, and configured to determine whether or not a response to the response request has been received from the corresponding first functional unit (112,122,123) of the another communication device, and a switching request unit configured to transmit, to the another communication device, a transfer-destination switching request for transferring packets that are supposed to be processed by the corresponding first functional unit (112,122,123) of the another communication device to the own device if the response has not been received from the corresponding first functional unit (112,122,123), the plurality of second functional units (112, 122, 123) is configured to process, in the computing devices (110, 120) on which they are respectively implemented, the packets transferred by the another communication device if the response has not been received.