PURPOSE: To display blood stream speed distribution in two dimensions in a legible form by giving different hues with respect to the positive and negative directions of the blood stream speed in a body to be checked, respectively, and displaying the luminance of each hue in a color on a screen in correspondence with the blood stream speed.

CONSTITUTION: A color display CRT34 displays speed distribution in colors in two dimensions. The average speed of a blood stream and the combination of deviation and the average speed are displayed in colors. When only a selection switch 20 is turned ON or only a tomographic image signal is outputted from a transceiver 10, the tomographic image is displayed on the screen of the color display 34 in a white color. With respect to the average speed data of the blood stream, which is obtained by a frame memory 16, different colors are given to a color operator 26 for the positive or negative directions of the speed, respectively. The specified luminance of the hue is changed in correspondence with the speed data at that time.