Image sensor having pupil-division fuction configured to output phase-difference signals in horizontal and vertical directions from different pixel groups and image capturing apparatus

An image sensor comprising a pixel array in which pixels are arranged in a matrix form, wherein

• phase-difference signals in a horizontal direction are output from a first pixel group of the pixel array via a first signal output line, and phase-difference signals in a vertical direction are output from a second pixel group, which is different from the first pixel group of the pixel array, via a second signal output line, and
• addition number of pixels of the phase-difference signals in the horizontal direction output via the first signal output line and addition number of pixels of the phase-difference signals in the vertical direction output via the second signal output line are different,
• wherein a plurality of column output lines including first column output lines and second column output lines are respectively arranged for each one column of the pixels, and the number of the second column output lines is larger than the number of the first column output lines.