When a terminal is moved to an area covered by a different switching node RNC of a radio access network, degradation of speech quality is prevented by returning a transcoder insertion connection to a transcoder-free-operation connection. When the terminal is moved and the switching node RNC of the radio access network is changed, a relocation is performed by inserting the transcoder, re-confirmation of parameter information of a bandwidth-compression coding system is requested for a local side switching node RNC and a remote side switching node RNC and, when the transcoder can be bypassed according to the confirmation, the transcoder is removed to return to the transcoder-free-operation connection mode.