PURPOSE: To always execute a focus detection with high accuracy by providing an illuminance distribution correction suppressing means for inhibiting or limiting a correction executed by an illuminance distribution correcting means only with respect to a saturated part, in case a signal of first and second images or a corrected output from the illuminance distribution correcting means is saturated.

CONSTITUTION: By dividing a signal an which has A/D-converted a CCD output signal of a first photoelectric converting element train (a signal bn which has A/D-converted a second photoelectric converting element train 5) by a correction coefficient (kn), the influence of an illuminance distribution can be eliminated, and an A/D conversion data An (or Bn) which has corrected an illuminance distribution error can be obtained easily. Also, even in case a DC component is contained in an illuminance difference between data A train by the first photoelectric converting element train 4 in the corrected A/D conversion data, and data B train by the second photoelectric converting element train 5, the correction can be executed simply. As for an output saturated by an A/D conversion level, a means for inhibiting to divide the A/D conversion output signal an (or bn) before the correction, by the correction coefficient (kn) is provided. In such a way, a focus detecting operation can be executed with high accuracy.