A mental fatigue detecting device to unintentionally detect mental fatigue by using blinking light is comprised of a light emitting unit (1) for irradiating blinking visible light, a lighting unit (2) for irradiating infrared light, an image picking-up unit (3) for picking up an infrared video image, and a control unit (4). The light emitting unit (3) applies simple and step-like variable blinking frequency visible light to an examinee (5). The image picking-up unit (3) carries out picking up an image including the eye of the examinee. The control unit (4) obtains time-sequential data of pupil diameters from a frame image composing the picked-up video image, obtains an examinee's flicker threshold frequency at the measurement time from pupil diameter fluctuations, compares the threshold frequency with an examinee's flicker threshold frequency at his or her non-fatigued state, and judges whether the examinee is in a mentally fatigued state or not.
MENTAL FATIGUE DETECTING METHOD AND DEVICE