An apparatus that includes an output unit having a photoelectric converting element and configured to produce a signal corresponding to light incident on the photoelectric converting element, a restricting unit configured to restrict a light receiving region of the photoelectric converting element to one of a first region and a second region, and a calculating unit configured to calculate a sensitivity of the first region, based on an output signal obtained from the output unit with respect to the first region to which the light receiving unit is restricted by the restricting unit, and on an output signal obtained from the output unit with respect to the second region to which the light receiving region is restricted by the restricting unit.