A focus detection apparatus, comprising, focus detection pixels that receive a pair of light fluxes resulting from pupil division of light flux, a memory that stores correction values in accordance with width of the imaging light flux in the pupil-division direction relating to a two-image interval value, and a controller having a focus detection section, a light flux width calculation section, and a defocus amount calculation section, wherein the light flux width calculation section calculates the width of the imaging light flux in the pupil-division direction, and the defocus amount calculation section calculates defocus amount of the photographing optical system based on the two-image interval value, wherein the focus detection section detects a first two-image interval value and corrects the first two-image interval value based on the correction values and the width of the imaging light flux in the pupil-division direction to obtain a second two-image interval value.