This fatigue estimation device (100) comprises: a fatigue estimation model (12) constructed in advance on the basis of data including a relationship between a physiological quantity outside an activity period of a person and the amount of human herpesvirus outside the activity period, the fatigue estimation model (12) being capable of outputting a fatigue degree estimated from the corresponding amount of human herpesvirus in response to an input of biometric information; a physiological quantity measurement unit (20) for measuring a physiological quantity of a subject (user (99)); and a fatigue estimation unit (10) for outputting the fatigue degree of the subject on the basis of the measured physiological quantity by using the fatigue estimation model (12).