An image pickup apparatus comprising: a plurality of pixels each including a photoelectric converting element; a plurality of capacitor which receive signals from the plurality of pixels at first terminals; a plurality of clamping switches for setting a second terminal of each of the plurality of capacitor into a predetermined electric potential; a plurality of first storing units for storing signals from the second terminals of the plurality of capacitor; a plurality of second storing units for storing the signals from the second terminals of the plurality of capacitor; a first common output line to which the signals from the plurality of first storing units are sequentially output; a second common output line to which the signals from the plurality of second storing units are sequentially output; and a difference circuit for operating a difference between the signal from the first common output line and the signal from the second common output line.