A focus detection apparatus configured to perform a focus detection using a pixel signal obtained by photoelectrically converting light passing through different pupil areas in an imaging optical system includes an acquirer configured to acquire the pixel signal, a signal generator configured to generate a plurality of focus detection signals corresponding to the different pupil areas using the pixel signal, and a focus detector configured to calculate a detected defocus amount based on the plurality of focus detection signals, and to calculate a corrected defocus amount by correcting the detected defocus amount based on a phase transfer function corresponding to the different pupil areas.