A waveform measuring apparatus includes: a digital filter for removing a large-amplitude changing component from an input signal and for outputting a resultant output signal with a small-amplitude noise component left therein; a window generating section for receiving a differential signal between this input signal and the resultant output signal of the digital filter and for generating a window indicating a position of an edge portion of the differential signal; and a ringing measurement section for extracting, from the resultant output signal of the digital filter, a portion of waveform which is indicated by the window generated by the window generating section and for measuring at least a peak-to-peak amplitude of the portion of waveform.