PURPOSE:To quantitatively judge the fine change of a grinding state, by displaying the reflection intensity of a cross-section containing a calculus. CONSTITUTION:Grinding concave surface vibrators 21a, 21b are connected to a pulser 33 to emit intensive ultrasonic pulses at a predetermined cycle. An ultrasonic probe 22 is connected to a transmitting and receiving circuit 31 and a receiving signal is reconstituted to a tomographic image in an image reconstitution circuit 32 to be displayed on a display circuit 36. A reflection intensity detection circuit 37 detects the reflection intensity of the image, where a calculus 25 is positioned, on the center axis of the picture of the tomographic image and the value thereof is displayed on the display circuit 36 as a numerical value or distribution simultaneously with the tomographic image. Since the calculus 25 is high in acoustic impedance as compared with other soft tissue, when said calculus 25 is looked on the tomographic image, the reflection intensity thereof is high and a hyperechoic image appears and the direction thereof shows dark shadow because an ultrasonic wave does not transmit through the calculus. When grinding advances during treatment, the reflection intensity lowers or the distribution of reflection spreads and the grinding state of the calculus can be judged.
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