A mental work load detector arranged to sense the electroencephalogram of a person and estimate a mental work load on the perceptual-motor system and a mental work load on the perceptual-central processing system separately from each other includes a electroencephalogram sensor arranged to sense the electroencephalogram of a rider, an eye fixation-related potential detector arranged to detect an eye fixation-related potential by analyzing the electroencephalogram and to detect a lambda response, an event-related potential measuring device arranged to measure an event-related potential in response to a sound from a speaker and to detect auditory p300, a lambda response comparator arranged to determine whether the lambda response has decreased, an auditory p300 comparator arranged to determine whether the auditory p300 has decreased, and a mental work load determiner arranged to determine that the mental work load on the perceptual-central processing system has increased if the lambda reaction and the auditory p300 has decreased and that the mental work load on the perceptual-central processing system has increased if the auditory p300 has decreased but the lambda response has not decreased.
