PROBLEM TO BE SOLVED: To detect the visual line of a subject without the need of calibration.SOLUTION: A device for transmitting a signal detects, from a result of imaging, a first rectangular form 20 that circumscribes one eye 10a of the subject and a second rectangular form 22 that circumscribes a cornea 10b of the eye 10a, the second rectangular form 22 being formed by four sides that are respectively parallel to four sides of the first rectangular form 20； normalizes a relative position of the second rectangular form 22 to the first rectangular form 20 by using a size of either of the first and second rectangular forms 20, 22 to obtain indexes x/W and &thetas；； and uses these indexes to detect a direction of a visual line of the subject. Since the size of the cornea 10b relative to the eye 10a is constant among individuals, using the normalized indexes x/w and &thetas； enables detection of the (direction of) visual line of the subject without the need of calibration even in cases of, for example, change in a distance between the device for transmitting a signal by detecting the visual line, and the subject, a shift in position, and the like.
