A portable terminal device (1) capable of easily evaluating mental fatigue comprises: an operation unit (4); an imaging unit for measuring ambient light (5); a display screen (2) or a light-emitting element (3) for presenting a flashing image or light while a flicker frequency of the flashing source is being monotonically changed from a start frequency to an ending frequency; and a recording unit for, when a user operates the operation unit (4) as the user perceives a flicker, recording the flicker frequency at the time point as a measured frequency, wherein: a first frequency datum, which is the measured frequency measured when the user is in a healthy condition, is associated with a first luminance datum, which is a measured ambient luminance, and the associated datum is stored in the recording unit, a proportion of decrease of a second frequency datum, which is the measured frequency measured when the user is not in a healthy condition, from the first frequency datum recorded in the recording unit and associated with the first luminance datum which has the same or similar order of magnitude to a second luminance datum, which is a measured ambient luminance, is calculated to evaluate a degree of fatigue of the user.