PROBLEM TO BE SOLVED: To appropriately estimate the degree of fatigue of a worker performing high load activity.SOLUTION: A biological information acquisition unit 121 acquires a heart rate of a living body. A fatigue degree estimation unit 126: estimates that a degree of fatigue of the living body is at a first stage, when a first fluctuation coefficient which is a coefficient of fluctuation in power spectral density with respect to frequencies in a first frequency range of the heart rate, exceeds a first threshold； and estimates that the degree of fatigue of the living body is at a second stage where the degree of fatigue of the living body is higher than that at the first stage, when a second fluctuation coefficient which is a coefficient of fluctuation in power spectral density with respect to frequencies in a second frequency range having the center frequency higher than that of the first frequency range, becomes lower than a second threshold, after the first fluctuation coefficient exceeds the first threshold.
