It is an object of this invention to realize an image sensing apparatus which satisfies both the requirements for focus detection performance and high-resolution, high image quality. In order to achieve this object, there is provided an image sensing apparatus characterized by comprising an image sensing device having a plurality of pixels, an optical element array having a plurality of optical elements made to correspond one by one to each set of a plurality number of pixels of a plurality of pixels of the image sensing device, and a focusing device which generates, for each of the plurality of optical elements, one pair of focus detection signals in the pixels from light passing through the optical element, and performs focusing operation on the basis of focus detection signals generated in pairs for each of the optical elements.