Abstract: A light beam passing a photographing lens is divided into two portions by a mirror in a camera body. One of the two divided light beams is directed to an eyepiece via a screen and pentagonal prism. The other divided light beam is reflected from a mirror and directed to a focus detection optical system constructed by a field view diaphragm, condenser lens, diaphragm mask and re-imaging lens, and an image in position corresponding to the range-finding field view is divided into two images by the optical system. An image sensor is arranged near the re-imaging surface which receives the two images formed by the focus detection optical system to photoelectrically convert a received signal and transfer data to a CPU. The CPU effects the focus detection operation containing the operation of interpolating the value of correlation between the two images by use of the self-correlation value of one of the two images based on detection data and drives the photographing lens to a focused position.