PURPOSE: To display each layer with color by producing a pulse with a pulse width corresponding to the time difference between two layer boundaries of a test body and by making it correspond to a color signal.

CONSTITUTION: A beamwise wave signal is emitted from an oscillating part 1 to the test body S, and its reflected wave is detected by a receiving part 2. The detected wave is amplified by an amplifier 3, and one frame is stored in a memory 16. The output of the memory 16 is amplified by a shaping amplifier 17, the first flip-flop (FF)18 is triggered by the output of said amplifier 17, an FF19 is done by the output of the FF18 and an FF20 by the FF19 in turn. The output P of the amplifier 17 is made correspond to the reflection from the layer boundary, and the respective flip-flops are made correspond to the respective layers. Outputs of the respective flip-flops 18W20 are made correspond to color signals, for example, red, green and blue color signals, and not only that the layer boundary is displayed but also that each layer is colored. In this way, the colored layer can be displayed.