PROBLEM TO BE SOLVED: To provide attenuation information of ultrasonic waves inside a subject capable of accurately discriminating a subject tissue. SOLUTION: An ultrasonic wave having two frequencies is transmitted from a transducer array to a tissue of a subject, a transmitted wave of the ultrasonic wave transmitted through the subject is received, and a reception signal is output. Based on the received signal, the attenuation rate, which is the attenuation amount of the ultrasonic wave per unit length when transmitting through the tissue of the subject, is obtained for each of the two frequencies, and is the rate of change of the attenuation rate between the two frequencies. Calculate the attenuation factor between frequencies. By using the attenuation rate between two frequencies, the tissue of the subject can be accurately identified. [Selection diagram] Figure 1【課題】被検体組織を精度よく判別可能な、被検体内部における超音波の減衰情報を提供する。【解決手段】振動子アレイから被検体の組織に、２つの周波数の超音波を送信し、被検体を透過した超音波の透過波を受信して受信信号を出力する。受信信号に基づいて、被検体の組織を透過する際の単位長さ当たりの超音波の減衰量である減衰率を２つの周波数についてそれぞれ求め、２つの周波数間の減衰率の変化率である２周波数間減衰率を求める。２周波数間減衰率を用いることにより、精度よく被検体組織を識別できる。【選択図】図１
