There is provided an image pickup apparatus comprising two-dimensionally arrayed pixels, a plurality of read-out channels each including a read-out circuit and an amplifier circuit, a parallel-serial conversion circuit which sequentially selects pixel signals output via the plurality of read-out channels and outputs a series of pixel signals, and a clamp unit which clamps the reset level included in an output signal from the read-out circuit in order to remove an offset generated in each read-out channel.