A communication device is connected to an end of a first network of a cascade topology, and also to a second network. This communication device transmits a first list including information of communication devices, in the first network, that are destinations of transmission of frames through the first network, to an opposing communication device, in the second network, located at another end of the first network, and receives, from the opposing communication device, a second list including information of communication devices, in the first network, that are destinations of transmission of frames from the opposing communication device through the first network. The communication device determines in which of the first list and the second list a destination of a frame is included, and when the destination of the frame is included in the second list, transmits the frame to the second network.