Patent US 5,396,336

An in-focus detecting device comprising a photo-electric converter element for converting an object image formed on the image receiving surface thereof through an image forming lens, a drive mechanism for controlling the focusing position of the lens, a focus degree detecting circuit for detecting the degree of focus in a prescribed distance measuring frame of the image receiving surface and the degree of focus outside the frame on the basis of the output signal of the photo-electric converter element, and a control circuit, responsive to the output of the focus degree detecting circuit representing that the degree of focus in the distance measuring frame is below a prescribed level, for comparing the degree of focus in the distance measuring frame with the degree of focus outside the frame to determine the direction of the image forming lens to be driven.