Picture and speech communication between plural terminals connected to different networks, such as a circuit-switched network and IP network. A converting apparatus 400 for control information or media information for picture/speech communications is provided across first and second terminals 301, 302 connected to respective different types of networks. Converting apparatus 400 includes control information converter 420, transcoder 450 and ability information converter 460. In case the ability information extracted from the decoding information, received from the first terminal 301, is not coincident to the ability information extracted from the call control information received from the second terminal 302, it is further checked whether or not there is picture format size coincidence. If the picture format size coincidence persists in one direction, processing is carried out for converting part of the decoding information or the control information, without causing the operations of the transcoder. In case there is no picture format size coincidence, the transcoder 450 is booted to convert the bitstream.