Two multiplexors select a first signal Ain and its inverted signal /Ain in the first half of a single cycle of a clock signal and Ain and /Ain, i.e., a differential signal pair, are differential-transmitted to two signal lines. On the other hand, the two multiplexors select a second signal Bin and its inverted signal /Bin in the second half and Bin and /Bin, i.e., a differential signal pair, are differential-transmitted to the two signal lines. Based on the transition probability of Ain and Bin or based on the mode information of a system, either Ain or Bin is selected and is differential-transmitted. As a result of such arrangement, when the transmission of one of Ain and Bin is not required, the other signal can continuously be differential-transmitted using an unoccupied signal line, which makes it possible to increase the rate of signal transmission without having to increase the number of signal lines.