A session mobility for moving a session held between a switching source device and a communication counterpart to a switching destination device other than the switching source device. The switching source device transmits media data relating to a session by multicast or broadcast prior to device switching. The switching destination candidate device receives the transmitted media data, and thereby switching destination determined device, in replace of the switching source device, outputs media data. Thus, a switching time from a switching source device to a switching destination device can be made fast such that a user cannot perceive it.