Provided is 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, without the need for an operator to perform a troublesome operation. The ultrasonograph is provided with a means for sending an ultrasonic beam into body tissue, a means for receiving an ultrasonic signal that has been reflected off the body tissue and a blood flow, a means for constructing a cross-sectional image of the body tissue from the received ultrasonic signal, a means for performing phase detection on an ultrasonic Doppler blood flow signal that has been reflected off the body tissue by the blood flow, a means for calculating a frequency component of the Doppler blood flow signal on which phase detection has been performed, 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 for measuring the heart rate of the test subject at a predetermining timing, and the ultrasonograph also includes an optimum sweep rate calculating means for calculating an optimum sweep rate based on the heart rate obtained by the heart rate measuring means, and an optimum sweep rate setting means for setting the sweep rate of at least either of the Doppler images and M-mode images.