An ultrasonograph that can automatically optimize the sweep rate of Doppler images and M-mode images according to the heart rate of a test subject. The ultrasonograph includes means for sending an ultrasonic beam into body tissue, a means for receiving an ultrasonic signal reflected off the body tissue and a blood flow, a means for constructing a cross-sectional image of the body tissue from the received signal, a means for performing phase detection on an ultrasonic Doppler blood flow signal, a means for calculating a frequency component of the Doppler blood flow signal, and a means for performing a sweeping display of the calculated frequency component as Doppler images in a time series. The ultrasonograph has a heart rate measuring means, an optimum sweep rate calculating means and an optimum sweep rate setting means.
