A timing-phase control system provided on the receiving side of a duobinary transmission system is adaptable to high-speed PCM repeater systems using a wide-band transmission medium such as a coaxial cable. The system includes a discriminating and regenerating circuit for recovering the transmitted digital signal by discriminating and regenerating in an appropriate timing phase based on an input equalized duobinary waveform, a phase varying circuit for varying the phase of a timing signal externally supplied to the discriminating and regenerating circuit, and a derivative waveform generating circuit. In one embodiment, the derivative waveform generating circuit is responsive to the output of the discriminating and regenerating circuit, and a multiplier multiplies the output of the derivative waveform generating circuit and the equalized duobinary waveform by each other in a predetermined phase relationship. In another embodiment, the derivative waveform generating circuit differentiates the equalized duobinary waveform on a time scale, and a multiplier multiplies the output of this differentiating circuit and that of the discriminating and regenerating circuit in a predetermined phase relationship. In either case, a low-pass amplifier amplifies the output of the multiplier to provide, with a suitable D.C. offset, a negative feedback signal to the phase varying circuit.