A signal transmitter apparatus generates three phase-shifted signals by shifting three transmission signals by predetermined phase shift amounts so that the phase shift amounts of the transmission signals are different from each other by 120 degrees. The signal transmitter apparatus generates three combined transmission signals and outputs the three combined transmission signals to the three transmission conductors, respectively, by combining each of pairs of the phase-shifted signals such that an inverted signal of a first phase-shifted signal is combined with a second phase-shifted signal, when each of the pairs of the phase-shifted signals includes the first and second phase-shifted signals among the three phase-shifted signals and phase shift amounts of the first and second phase-shifted signals are different from each other by 120 degrees. The signal receiver apparatus generates three receiving signals based on received three combined transmission signals, and detects the decoded signals of the transmission signals based on the receiving signals.