An object of the present invention is to accurately estimate a sleep stage of a measurement subject without imposing a burden on the measurement subject. Body movement or pressure change during sleep of a measurement subject is detected as biological data. Then, the detected biological data is subjected to frequency analysis to detect an approximate heartbeat frequency component, and an approximate heartbeat low frequency component lower than the approximate heartbeat frequency component is detected as a component corresponding to a circadian rhythm component. Further, the sleep stage is determined from the value obtained by correcting the detected approximate heartbeat frequency component based on the fluctuation of the approximate heartbeat low frequency component. [Selection] Figure 4【課題】被測定者に負担をかけずに、被測定者の睡眠段階を精度良く推定する。【解決手段】被測定者の睡眠中の体動または圧力変化を生体データとして検出する。そして、検出した生体データを周波数解析して、近似心拍中周波成分を検出すると共に、近似心拍中周波成分よりも低い近似心拍低周波成分を、サーカディアンリズム成分に相当する成分として検出する。さらに、検出した近似心拍中周波成分を、近似心拍低周波成分の変動に基づいて補正した値から、睡眠段階を判定する。【選択図】図４
