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 an eye according to the line-of-sight reliability; 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.