A line-of-sight detection device, comprising: at least one camera configured to capture an image of a face of a subject irradiated with detection light emitted from at least one light source; an image data acquisition unit configured to acquire image data of the image captured by the camera; a line-of-sight detection unit configured to detect a line of sight of the subject by calculating a corneal curvature center based on a pupil center and a corneal reflection center which are included in the acquired image data and obtaining a line-of-sight vector connecting the pupil center and the corneal curvature center; an image processing unit configured to perform image processing on the image data to generate a contour image of the face and an eyeglasses reflection image indicating a reflection image of the at least one light source on eyeglasses worn on the face; a display device in which the contour image and the eyeglasses reflection image are displayed; and a display controller configured to cause the display device to display the contour image and the eyeglasses reflection image in a different display form in a composite image in which the contour image and the eyeglasses reflection image are combined, wherein the contour image is an image that allows the subject or a measurer of the line-of-sight detection device to recognize or estimate, when viewing the contour image displayed in the display device, a position of a pupil from the contour image to thereby allow the subject or the measurer to adjust a position or an orientation of the face thereof or adjust a position or an orientation of the eyeglasses such that the reflection image of the light source and an eye of the subject do not overlap in a visual field area of the camera while viewing the composite image displayed on the display device, and after adjusting the position or the orientation of the face of the subject or the position or the orientation of the eyeglasses, the line-of-sight detection unit is configured to detect the line of sight of the subject. at least one camera configured to capture an image of a face of a subject irradiated with detection light emitted from at least one light source; an image data acquisition unit configured to acquire image data of the image captured by the camera; a line-of-sight detection unit configured to detect a line of sight of the subject by calculating a corneal curvature center based on a pupil center and a corneal reflection center which are included in the acquired image data and obtaining a line-of-sight vector connecting the pupil center and the corneal curvature center; an image processing unit configured to perform image processing on the image data to generate a contour image of the face and an eyeglasses reflection image indicating a reflection image of the at least one light source on eyeglasses worn on the face; a display device in which the contour image and the eyeglasses reflection image are displayed; and a display controller configured to cause the display device to display the contour image and the eyeglasses reflection image in a different display form in a composite image in which the contour image and the eyeglasses reflection image are combined, wherein the contour image is an image that allows the subject or a measurer of the line-of-sight detection device to recognize or estimate, when viewing the contour image displayed in the display device, a position of a pupil from the contour image to thereby allow the subject or the measurer to adjust a position or an orientation of the face thereof or adjust a position or an orientation of the eyeglasses such that the reflection image of the light source and an eye of the subject do not overlap in a visual field area of the camera while viewing the composite image displayed on the display device, and after adjusting the position or the orientation of the face of the subject or the position or the orientation of the eyeglasses, the line-of-sight detection unit is configured to detect the line of sight of the subject.