PURPOSE: To generate an optimum binary coded signal corresponding to the luminance distribution of various objects by counting pulse signals and ending the integration, i.e., binary coding, at the point of the time when the count value attains a prescribed value.

CONSTITUTION: The output of a comparator 50 inverts to the signal of a high level at the point of the time when the output voltage of an adder falls bellow the voltage to be impressed to the non-inversion input terminal of the comparator 50. The operation of a control circuit 43 is stopped and the integration action is consequently ended. The data outputted from a shift register 41 in this stage is inputted as the binary coded signal by a phase difference detecting circuit 44 at the same instant and the deviation quantity (phase difference) of the respective object on respective photodetector arrays is detected in accordance with said signal.