An imaging apparatus comprising: a pixel unit including at least three photoelectric conversion units (202-1n, 202-2n, 202-3n, 202-4n), and an amplifying transistor provided in common to the at least three photoelectric conversion units, and configured to output a signal based on a charge generated by any one of the at least three photoelectric conversion units to a signal line; a constant current source connected to the signal line; and a control unit configured to set the pixel unit to a selected state or a non-selected state according to an electric potential of a control electrode of the amplifying transistor, and configured to sequentially output signals based on the at least three photoelectric conversion units, wherein the pixel unit is set to the selected state by resetting the control electrode of the amplifying transistor to an electric potential that allows the amplifying transistor to operate as an amplifier in conjunction with the constant current source, and wherein the pixel unit is set to the non-selected state by resetting the control electrode of the amplifying transistor to an electric potential that does not allow the amplifying transistor to operate as an amplifier in conjunction with the constant current source; characterized in that the control unit is configured to perform in an alternate manner, an operation of setting the pixel unit to the non-selected state prior to an operation of outputting the signal from the pixel unit based on one of the photoelectric conversion units, and an operation of outputting the signal based on another one of the photoelectric conversion units without intervening the operation of setting the pixel unit. a pixel unit including at least three photoelectric conversion units (202-1n, 202-2n, 202-3n, 202-4n), and an amplifying transistor provided in common to the at least three photoelectric conversion units, and configured to output a signal based on a charge generated by any one of the at least three photoelectric conversion units to a signal line; at least three photoelectric conversion units (202-1n, 202-2n, 202-3n, 202-4n), and an amplifying transistor provided in common to the at least three photoelectric conversion units, and configured to output a signal based on a charge generated by any one of the at least three photoelectric conversion units to a signal line; a constant current source connected to the signal line; and a control unit configured to set the pixel unit to a selected state or a non-selected state according to an electric potential of a control electrode of the amplifying transistor, and configured to sequentially output signals based on the at least three photoelectric conversion units, wherein the pixel unit is set to the selected state by resetting the control electrode of the amplifying transistor to an electric potential that allows the amplifying transistor to operate as an amplifier in conjunction with the constant current source, and wherein the pixel unit is set to the non-selected state by resetting the control electrode of the amplifying transistor to an electric potential that does not allow the amplifying transistor to operate as an amplifier in conjunction with the constant current source; perform in an alternate manner, an operation of setting the pixel unit to the non-selected state prior to an operation of outputting the signal from the pixel unit based on one of the photoelectric conversion units, and an operation of outputting the signal based on another one of the photoelectric conversion units without intervening the operation of setting the pixel unit.