There is provided a jitter estimating apparatus for calculating phase noise waveform of an input signal and for estimating a peak value, a peak-to-peak value and a worst value of jitter of the input signal, and probability to generate jitter based on the phase noise waveform. Timing jitter sequence, period jitter sequence, and cycle to cycle period jitter sequence of the input signal are calculated and the peak value and the peak to peak value for each jitter, as well as probability to generate jitter may be estimated.