A phase-difference detecting image pickup element performs focus detection even if the position of an exit pupil with respect to the image pickup element changes. A pixel pair receives an object light beam transmitted through a pair of portion areas whose areas become the same in an exit pupil at a particular distance from the image pickup element. The pixel pair includes light-intercepting portions that define the pair of portion areas. A different pixel pair whose light-intercepting portions are different so that the areas of the pair of portion areas in the exit pupil the particular distance from the image pickup element are the same. By this, even if the position of the exit pupil is changed by, for example, a lens replacement, focus detection can be performed by a phase-difference detection method by selecting a pixel pair in accordance with the position of the exit pupil.