In a signal transmitter for a multiple differential transmission system including a signal transmitter and a signal receiver connected via three signal lines, first and second differential drivers generate first and second output signals of bipolar four values and having a first signal voltage level, and inverted first and second output signals, responsive to first and second bit information signals. A third differential driver generates a third output signal of bipolar four values having a second signal voltage level, and an inverted third output signal, responsive to a third bit information signal. The first output signal and the inverted third output signal are combined and transmitted to the first signal line, the second output signal and the inverted first output signal are combined and transmitted to the second signal line, and the third output signal and the inverted second output signal are combined and transmitted to the third signal line.