There is provided a jitter measuring apparatus for measuring jitter in a signal-under-measurement, including a pulse generating section having first pulse generating means for detecting edges of the data-signal-under-measurement to output a first pulse signal having a pulse width set in advance corresponding to the edge and second pulse generating means for detecting boundaries of data sections where data values do not change in the data-signal-under-measurement to output a second pulse signal having a pulse width set in advance over the edge timings of the boundaries of the detected data sections and a jitter calculating section for calculating timing jitter in the data-signal-under-measurement based on the first and second pulse signals.