[Problem] To provide means by which sleep states can be measured, observed, or evaluated easily. [Solution] A sleep state measurement device that includes a phase coherence calculating means for calculating phase coherence on the basis of the instantaneous phase difference between the instantaneous phase of heart rate variability acquired from a sleeping animal and the instantaneous phase of the breathing pattern of the animal for the same time series as the heart rate variability.
Device and method for measuring sleep state, phase coherence calculation device, body vibration signal measurement device, stress level measurement device, sleep state measurement device, and cardiac waveform extraction method