PURPOSE: To suppress a picture blur to the minimum and to obtain a stable picture by controlling a focus in a distance measuring range of the whole first, in a pupil dividing method, and switching to a narrow distance measuring range of a part whose output level is high, of a photoelectric element.

CONSTITUTION: As for an output of each photoelectric element of a photodetecting array D, the same signal is stored in shift registers R1, R2 through a transfer device T. An, An+1, Bn and Bn+1 are transferred to an algorithm processor P1 and P2 by a clock from cables K7, K8. Basing on S=Σ{(An-Bn+An+1-Bn+1). (An-An+1-Bn-Bn+1)}, the first extent of shift corresponding to the minimum value of S in all areas of the photoelectric element is derived by the P1, the second extent of shift corresponding to the minimum value of S in a small section centering around the maximum signal of A1WAn and B1WBn is derived by the P2, compared with a reference value by a selector V, and a lens L0 is controlled by the selected first or second extent of shift.