1. An image-capturing device comprising: a plurality of first pixels disposed along a first direction; a plurality of second pixels different from the first pixels disposed along the first direction in admixture with the plurality of first pixels; and an adder that adds a plurality of outputs provided by a plurality of first selected pixels selected from the plurality of first pixels to each other and a plurality of outputs provided by a plurality of second selected pixels selected from the plurality of second pixels to each other in such a manner that outputs provided by the first pixels and outputs provided by the second pixels are not added one to another, wherein disposition of the plurality of second pixels conforms to positional relationship of the plurality of first selected pixels in the plurality of first pixels.