PURPOSE: To easily detect an abnormal bloodstream, even if light, by comparing the average speed and dispersion detected from the bloodstream signal with the preset threshold values respectively, and displaying the color display picture element of the bloodstream corresponding to the portion where the average speed and dispersion exceed the threshold values in the special hue other than the normal display.

CONSTITUTION: Ultrasonic waves from a probe 1 are reflected by an organism and received by the probe 1, and the reception signal is inputted to two mixers 4 via an adder 3. Reference signals different in phase by 90° are fed to the mixers 4 from a phase converter 5, and products of the reference signals and the reception signals are obtained. Only the bloodstream signal is detected by a band filter 6, the Doppler deviation frequency is determined by a frequency analyzer 7, and the average speed, dispersion, and power in the organism are detected. The spread of the dispersion is normalized by a normalizing means 11. The detection portion where the speed and dispersion are judged to exceed the preset threshold values by a threshold value judgment section 12 is displayed in the special hue on a display section 10.