1. An image-capturing apparatus, comprising: a micro-lens array that includes a plurality of micro-lenses arrayed therein; an image sensor that includes arrayed therein a plurality of pixels that capture a plurality of pupil projection images, each corresponding to a pupil of an optical system projected via one of the plurality of micro-lenses as a light flux from the optical system passes through the micro-lens array; a photographic image generation unit that generates, based upon an output from the image sensor, a photographic image including a partial image corresponding to each of the plurality of pupil projection images; and an arithmetic operation unit that executes position calculation to determine a center position of the partial image by scanning the photographic image in reference to a reference image corresponding to the partial image.