An image sensor comprising: a plurality of pixels disposed in a two-dimensional matrix form and configured to receive light from outside, to generate corresponding imaging signals in accordance with an amount of the received light, and output the imaging signals to corresponding ones of a plurality of vertical transfer lines; a reference signal generation unit configured to generate a reference signal in accordance with a predetermined voltage and to output the reference signal to a dedicated vertical transfer line provided separately from the plurality of vertical transfer lines, characterized by further comprising a transfer unit configured to sequentially transfer, to a horizontal transfer line, the reference signal from the dedicated vertical transfer line and the imaging signals from the corresponding ones of the plurality of vertical transfer lines, during different transferring periods, for each row of the two-dimensional matrix; and an output unit configured to input the reference signal and the imaging signals from the horizontal transfer line, wherein the output unit comprises: a first holding unit configured to hold the reference signal; a second holding unit configured to to sequentially hold the imaging signals; and a switching unit that is connected to each of the first holding unit and the second holding unit, and is configured to sequentially switch between the reference signal held by the first holding unit and the imaging signal held by the second holding unit to output a switched signal, for each imaging signal. a plurality of pixels disposed in a two-dimensional matrix form and configured to receive light from outside, to generate corresponding imaging signals in accordance with an amount of the received light, and output the imaging signals to corresponding ones of a plurality of vertical transfer lines; a reference signal generation unit configured to generate a reference signal in accordance with a predetermined voltage and to output the reference signal to a dedicated vertical transfer line provided separately from the plurality of vertical transfer lines, characterized by further comprising a transfer unit configured to sequentially transfer, to a horizontal transfer line, the reference signal from the dedicated vertical transfer line and the imaging signals from the corresponding ones of the plurality of vertical transfer lines, during different transferring periods, for each row of the two-dimensional matrix; and an output unit configured to input the reference signal and the imaging signals from the horizontal transfer line, wherein the output unit comprises: a first holding unit configured to hold the reference signal; a second holding unit configured to to sequentially hold the imaging signals; and a switching unit that is connected to each of the first holding unit and the second holding unit, and is configured to sequentially switch between the reference signal held by the first holding unit and the imaging signal held by the second holding unit to output a switched signal, for each imaging signal. a first holding unit configured to hold the reference signal; a second holding unit configured to to sequentially hold the imaging signals; and a switching unit that is connected to each of the first holding unit and the second holding unit, and is configured to sequentially switch between the reference signal held by the first holding unit and the imaging signal held by the second holding unit to output a switched signal, for each imaging signal.