An image sensor comprises: a pixel region including a plurality of microlenses arranged in a matrix, and a plurality of photoelectric conversion portions provided for each of the microlenses; a plurality of amplifiers that apply a plurality of different gains to signals output from the pixel region; and a scanning circuit that scans the pixel region so that a partial signal and an added signal are read out, the partial signal being a signal from some of the plurality of photoelectric conversion portions, and the added signal being a signal obtained by adding the signals from the plurality of photoelectric conversion portions.