To reliably determine the direction of the subject's
gaze. [Solution] The
gaze direction detection device 1 comprises a camera 10 that acquires a face image by capturing the face of subject A, and an
image processing device 20 that processes the face image acquired by the camera 10 to determine the
gaze direction of subject A. The
image processing device 20 detects the three-dimensional positions of the
right pupil, left
pupil, and
nose based on the face image, identifies the three-dimensional position of the intersection of a second straight line that passes through the three-dimensional position of the
nose and intersects perpendicularly with a first straight line connecting the three-dimensional positions of the
right pupil and the three-dimensional positions of the left
pupil, and the first straight line, and determines the gaze direction of subject A using the first distance between the three-dimensional position of the intersection and the three-dimensional position of the
right pupil, the second distance between the three-dimensional position of the intersection and the three-dimensional position of the left
pupil, and the third distance between the three-dimensional position of the intersection and the three-dimensional position of the
nose.