1. A pupil detection method comprising: a first step of acquiring a first image by taking a facial image of a subject using a first camera; a second step of acquiring a second image by taking a facial image of the subject using a second camera; a third step of extracting one or more first image candidate points serving as candidates for a pupil of the subject from the first image; a fourth step of extracting one or more second image candidate points serving as candidates for a pupil of the subject from the second image; a fifth step of determining whether a combination of one of the first image candidate points and one of the second image candidate points corresponds to the same point in a three-dimensional space; a sixth step of extracting two or more space candidate points by setting the point in the three-dimensional space corresponding to the combination of the first image candidate point and the second image candidate point determined as corresponding to the same point in three-dimensional coordinates as the space candidate point; a seventh step of selecting a pair of two space candidate points among the extracted space candidate points and calculating a distance between the selected pair of two space candidate points for a plurality of pairs of space candidate points; an eighth step of excluding a pair of space candidate points where the calculated distance between the pair of space candidate points is not within a specified range; and a ninth step of determining one or more pairs of space candidate points among the pairs of space candidate points having not been excluded and determining that a pair of pupils of the subject exist at positions of the determined one or more pairs of space candidate points.