A focus detection apparatus includes an image sensor including pixels for focus detection for receiving a pair of respective light beams transmitted through different pupil areas of a photographing lens to output a pair of signals; an acquisition unit for acquiring exit window information on the photographing lens; an arithmetic circuit for calculating a tilt for detection area in the detecting position, depending on an image height for a detecting position in which a focus state is detected and on the exit window information; and a calculation unit for calculating the shape of the detection area depending on the calculated tilt, in which the defocus amount is detected on the basis of a phase difference between the pair of signals obtained from pixels for focus detection included in the calculated detection area.