PURPOSE: To calculate the sure attenuation degree of an ultrasonic wave by finding out the reduction of amplitude at two time points by an area setting means for a substance to be measured which corresponds to at least two time points after the transmission of an ultrasonic pulse, an echo signal accumulating means and an operation means.

CONSTITUTION: An ultrasonic wave transducer 2 is driven by a transmission circuit 1 at prescribed driving voltage and frequency and an ultrasonic pulse 17 is transmitted into a living body 14. A part of the pulse 17 is reflected by scattered light 15, transmitted into the living body again and received by the transducer 2 as a received echo 18. A pulse 18a is transmitted through a scattering body 15 then transmitted into the deep portion of the living body. An operation circuit 11 calculates the attenuation degree of echo amplitude from the received ultrasonic echo by using memory circuits 9, 10 and a monitor display 7 displays the calculated value as a visual image. Thus, the attenuation degree of the ultrasonic wave in the area of the substance to be measured which corresponds to at least two time points can be calculated from the linear ramp obtained from linear approximation.