The invention provides a focus detection apparatus comprising: an image sensor configured to convert an object image, the image sensor having a focus detection pixel for receiving a light beam that has passed through a partial area, which is a division of an exit pupil of an optical system for forming an object image; addition unit configured to multiply outputs of a plurality of the focus detection pixels included in a predetermined area of the image sensor by a weighting coefficient corresponding to a position of the focus detection pixel, and perform addition; and defocus amount calculation unit configured to calculate a defocus amount based on a pair of phase-difference detection signals generated based on an output of the addition unit.