The present invention uses a time series waveform of biological signal information (back surface pulse wave) including sound and vibration of the organism collected from the back of the person. Dorsal surface pulse wave is a pressure oscillation resulting from the motion of the heart and aorta, including the contraction and diastolic information of the ventricle and the elasticity information of the vascular wall which serves as an auxiliary pump of circulation, and it is regarded as a vibration system including damping of both viscous damping and solid friction .In addition, the flow rate varies with the flow rate of blood delivered from the heart (the amount of one beat), which is reflected in the amplitude of the time series waveform of the back surface pulse wave. Then, by applying the method of calculating the damping ratio of the free attenuation vibration waveform, the amplitude of the two wave components in one cardiac cycle, and the amplitude of the two wave components in the amplification period are compared, and the biological state, especially the state of the living state related to the blood pressure, is grasped. .本発明は、人の背部から採取される生体の音及び振動を含む生体信号情報（背部体表脈波）の時系列波形を用いる。背部体表脈波は、心臓と大動脈の運動から生じる圧力振動であり、心室の収縮期及び拡張期の情報と、循環の補助ポンプとなる血管壁の弾力情報を含んでおり、粘性減衰摩擦と固体摩擦の両種の減衰を含む振動系と捉えられる。また、心臓から送り出される血液の流量（１回拍出量）に対応して変動し、この流量の変動は、背部体表脈波の時系列波形の振幅に反映される。そこで、自由減衰振動波形の減衰比を算出する解法を応用し、１心周期内の所定の波形成分、好ましくは増幅期における２つの波形成分の振幅を対比することで、生体状態、特に、血圧と関連した生体状態を把握することができる。
