A muscle fatigue output device is provided with a myoelectric measurement unit that acquires myoelectricity of a user, and a main control unit that determines fatigue of a muscle of the user on the basis of the myoelectricity. The main control unit (a) uses the myoelectricity to acquire a value for a frequency characteristic of the myoelectricity, (b) uses the myoelectricity to acquire a value for an amplitude characteristic of the myoelectricity, (c) acquires a ratio between the value for the frequency characteristic and the value for the amplitude characteristic as an index for the fatigue of the muscle of the user, and (d) outputs information regarding the fatigue of the muscle of the user, on the basis of the index for the fatigue of the muscle of the user.