An image sensor comprises: a first semiconductor including a plurality of pixels two-dimensionally arranged, and a plurality of divided output lines, in a first direction, configured to read out pixel signals from the plurality of pixels in the first direction; and a second semiconductor including a plurality of signal processing units, corresponding to the plurality of output lines, respectively, configured to process the readout pixel signals, and a readout unit configured to read out the signals output from the signal processing units in a second direction, wherein the first semiconductor and the second semiconductor are stacked, and the plurality of output lines and the plurality of signal processing units are connected in correspondence with each other.