1. A line-of-sight detection apparatus comprising: a detection unit configured to detect a face from image data; a first extraction unit configured to extract a feature amount corresponding to a direction of the face from the image data; a calculation unit configured to calculate a line-of-sight reliability of each of a right eye and a left eye based on the face; a selection unit configured to select at least one eye of which the calculated line-of-sight reliability is higher than a threshold for each eye, from the right eye and the left eye; a second extraction unit configured to extract a feature amount of an eye region of the selected eye from the image data; and an estimation unit configured to estimate a line of sight of the face based on the feature amount corresponding to the face direction and the feature amount of the eye region of the selected eye; a generation unit configured to generate a low resolution face image and a high-resolution face image from the detected face, wherein the first extraction unit is configured to extract a feature amount corresponding to a direction of the face from the low-resolution face image, and a second extraction unit configured to extract a feature amount of an eye region of the selected eye from the high-resolution face image.