An image sensor includes a pixel array. The pixel array includes a plurality of sensing pixels and at least two focusing pixels adjacent to each other. Each of the sensing pixels is configured to output an image signal corresponding to an amount of light incident on the sensing pixels. The at least two focusing pixels are configured to output a focusing signal corresponding to a phase difference between light incident on the at least two focusing pixels. Each of the sensing pixels and the at least two focusing pixels includes a semiconductor layer including a photodetecting device. Each of the sensing pixels includes a light guide which guides incident light toward the photodetecting device, and each of the at least two focusing pixels does not include the light guide.