PROBLEM TO BE SOLVED: To calculate the thickness of a tissue of a living body using the principle of photometry, and also accurately detect a motion of the body, which is a cause of hampering the photometry.SOLUTION: The extinction of a first light beam is acquired based on a first intensity signal corresponding to the intensity of the first light beam, the first light beam containing a first wavelength λtransmitted through or reflected from a tissue of a living body. The extinction of a second light beam is acquired based on a second intensity signal corresponding to the intensity of the second light beam, the second light beam containing a second wavelength λtransmitted through or reflected from the tissue. The thickness of the tissue is calculated based on the ratio between the first extinction and the second extinction. A motion of the living body is detected based on temporal change of the tissue thickness.SELECTED DRAWING: Figure 4【課題】フォトメトリの原理を用いつつ生体の組織厚を算出するだけでなく、当該フォトメトリを阻害する一因である当該生体の体動を正確に検出する。【解決手段】生体の組織を透過あるいは反射した第一波長λ１を含む第一の光の強度に対応する第一強度信号に基づいて、当該第一の光の減光度が取得される。当該組織を透過あるいは反射した第二波長λ２を含む第二の光の強度に対応する第二強度信号に基づいて、当該第二の光の減光度が取得される。当該第一減光度と当該第二減光度の比に基づいて、当該組織の組織厚が算出される。当該組織厚の経時変化に基づいて、当該生体の体動が検出される。【選択図】図４
