PROBLEM TO BE SOLVED: To provide a device that can grasp of the increase and decrease of a periodic fatigue degree by using an accelerometer portable in daily life.SOLUTION: A portable fatigue degree determining device includes an acceleration sensor 2 and calculation means. The calculation means has: a daily average walking speed calculation function for calculating a daily average walking speed (hereinafter referred to as the daily average walking speed) from acceleration data detected by the acceleration sensor 2 a function for associating the daily average walking speed with the working days or the non-working days showing what day of the continuous working days or the non-working days, by entering continuous working days or non-working days concerning the working days and the non-working days repeated periodically a function for calculating a correlation coefficient between the working days or the non-working days and the daily average walking speed and a fatigue degree determination function for determining the fatigue accumulation tendency in the working day or the fatigue accumulation tendency in the non-working day, based on the correlation coefficient.SELECTED DRAWING: Figure 1
