A video/audio signal transmitted from a transmission source 10 to transmission destinations 20A and 20B is stored repeatedly for a predetermined time period. Thus, for example if the video/audio signal is overwritten at predetermined timing, it is sufficient to have a small storage capacity for the video/audio signal. Also, the video/audio signal on which an error has occurred remains without being overwritten at the time of determination that an error has occurred. Accordingly, by transmitting this signal to a predetermined destination, a detailed error analysis can be made promptly on the basis of the transmitted video/audio signal.