A focus adjustment apparatus includes a diaphragm aperture adjustment unit configured to adjust a diaphragm aperture area of a photographic lens, a focus detection unit configured to detect a defocusing amount by using a pair of light fluxes passed through different areas of the photographic lens, a detection result correction unit configured to calculate, during focus detection after the diaphragm aperture area has changed by a value equal to or larger than a predetermined value, a reduced defocusing amount correction value with respect to the defocusing amount, and a focus adjustment unit configured to execute control to adjust a focus based on the defocusing amount correction value.