Abstract: A digital circuit which transmits information by a multilevel signal having at least two values. A waveform shaping section is provided to which at least first and second presumption values for defining at least first and second presumption ranges based on said at least two values, respectively, are set. The waveform shaping section performs a waveform shaping for eliminating higher harmonic components of a waveform in each of the presumption ranges and performs a waveform shaping for maintaining abrupt changes of the waveform in a transition period from one of the presumption ranges to another.