Transmitting and receiving ultrasound with repetition frequency that corresponds to velocity range indicating the measurable velocity to and from a diagnostic site that contains moving fluid within a body to be examined. Generating Doppler spectrum image showing velocity of moving fluid based on signals obtained from transmission and reception of ultrasound. Storing modeled value based on model correlating standard blood velocity waveform with an ECG waveform. Calculating measured blood velocity waveform based on spectrum image of a specified patient. Acquiring ECG waveform at timing corresponding to measured blood velocity waveform. Estimating blood velocity waveform excluding effects of valve signals of patient based on measured blood velocity waveform, ECG waveform, and modeled value. Comparing measured blood velocity waveform with estimated blood velocity waveform, to exclude excess parts of the difference over a threshold from measured blood velocity waveform, and to interpolate excluded parts of measured blood velocity waveform.