1. An image-capturing device comprising: an image-capturing unit; and an image processing unit, wherein the image-capturing unit includes image-capturing element units arranged in a two-dimensional matrix form, and each of the image-capturing element units includes: a first image-capturing element including a first filter and a first photoelectric conversion element, and configured to receive light in a first wavelength band; a second image-capturing element including a second filter and a second photoelectric conversion element, and configured to receive light in a second wavelength band having a peak wavelength longer than a peak wavelength of the first wavelength band; a third image-capturing element including a third filter and a third photoelectric conversion element, and configured to receive light in a third wavelength band having a peak wavelength longer than a peak wavelength of the second wavelength band; and a fourth image-capturing element including a fourth filter and a fourth photoelectric conversion element, and configured to receive light in the first wavelength band, the second wavelength band, and the third wavelength band, and wherein a light transmission rate of the fourth filter is less than a light transmission rate of the first filter, a light transmission rate of the second filter, and a light transmission rate of the third filter, and the image processing unit generates high sensitivity image data in accordance with outputs from the first image-capturing element, the second image-capturing element, and the third image-capturing element, and generates low sensitivity image data in accordance with an output from the fourth image-capturing element, and the image processing unit further generates a combined image using high sensitivity image data corresponding to a low illumination image area in the low illumination image area obtained from the low sensitivity image data or the high sensitivity image data, and using low sensitivity image data corresponding to an high illumination image area in the high illumination image area obtained from the low sensitivity image data or the high sensitivity image data.