PURPOSE: To accurately measure the heart rate cycle of an embryo, by detecting the max. power peak within the specific frequency range of a power spectrum and calculating time difference from the frequency of said max. power peak and determining the position range before and after said power peak as the time difference range corresponding to the heart rate cycle of the embryo.

CONSTITUTION: The autocorrelation function R(τ) obtained from an autocorrelation operating means 2 shows what degree an embryo heart rate signal X(t) has the similarity with respect to the heart rate signal at the time separated by time difference τ from the time of said signal X(t). The output power spectrum P(f) of a means 8 obtained from a digital signal or the Fourier transform of the autocorrelation function shows the intensity of the appearance of the frequency of the signal. Therefore, the range of the corresponding time difference τ is determined from the frequency (f) bringing the power spectrum P(f) to the max. peak and the time difference τ of the peak of the correlation value R(τ) within said range and, when a heart rate cycle is calculated from said time difference τ, the heart rate cycle considered to be correct judging from both aspects of wave form similarity and cyclicity is discriminated and a correct embryo heart rate cycle is calculated.