There is provided a clock generator for generating a modulation waveform which is high in the effect of suppressing a spectrum and making a circuit scale smaller than a modulation system using the Hershey-kiss waveform. More specifically, a modulation waveform generation unit generates a tangent waveform or a tangent+triangular waveform as an SSCG modulation waveform and provides an oscillator with a signal in which the SSCG modulation waveform is combined with the output of a low pass filter of a PLL loop.