A fatigue degree measurement device includes a living body signal peak value detecting step to detect the peak values of respective cycles of the original waveform of the living body signal data; a power value calculating step to calculate the difference between a peak value on the upper limit side and a peak value on the lower limit side for every prescribed time period from respective peak values obtained by the living body signal peak value detecting step to set the difference as a power value; and a power value inclination calculating step to determine the inclination of the power value, to calculate an integral value by absolute value treatment of the time series signals of the inclination of the power values to determine the integral value as the degree of fatigue.