An image capturing apparatus that uses an image sensor having pixels for capturing an image and pixels for detecting a phase difference. If, in the case where it is determined that it is necessary to restart focus detection during recording of a moving image, an opening diameter of an aperture is not an opening diameter at which phase-difference detection type AF using the pixels for detecting a phase difference can be performed, the aperture is changed to an opening diameter at which phase-difference detection type AF can be performed during focus detection. Thus, even if a photographic lens that does not support driving within a minute range is mounted, a focus detection operation suitable for shooting a moving image can be performed.