In order to make it possible to suppress attenuation of a data signal waveform without extra power consumption in high-speed transmission by using a high-speed clock, a data transmission system of the present invention includes a sending unit that outputs a reference signal generated by delaying a clock signal and a modulation signal which is either a signal the phase of which is delayed with respect to the reference signal in accordance with a state of a data signal or the clock signal, a transmission unit that transmits the reference signal and modulation signal, a peaking unit that suppress a development of peaking by applying inductor peaking to a signal on a transmission path, and a receiving unit that demodulates the data signal by detecting a phase difference between the reference signal and the modulation signal and outputs information on the data signal.