PURPOSE: To improve focusing responsiveness by varying the ratio between the detected distance between images of an object to be photographed and the driving extent of a lens according to a front-focus or rear-focus state.

CONSTITUTION: An output (s) corresponding to the distance between, for example, two images of the object to be photographed obtained through, for example, two photodetecting sensor and comparator varies to a high or low level according to the rear-focus or front-focus state to open an AND gate 32 and an AND gate 31 connected to an inverter. Then, the counting period of a counter 21 for controlling the extent of lens drive is controlled in the period of a clock CP from an oscillator 23 or in a half the period of the clock CP passed through an FF30. Therefore, the ratio between the interimage detected distance of the object to be photographed and the extent of lens drive is varied according to the front-focus or rear-focus to improve the focusing responsiveness regardless whether the lens is moved in or out.