The objective of the present invention is to suppress deterioration of call quality caused by transcoding without interrupting a call even if a codec used by one of the terminals during communication is changed. A modification determination unit (608), in the case of detecting a modification of a codec used by one terminal of two terminals, determines whether or not to constrain the bandwidth of the first codec using a first codec of the other terminal, and a second codec after modification by the first-mentioned one of the terminals. A signaling generation unit (610) transmits, to the other terminal, signaling for limiting the bandwidth if the bandwidth is to be limited.