Abstract: An image input system comprises a solid state image pickup device and a preprocessor (3) for performing correlated double sampling amplification on an output signal of the solid state image pickup device and outputting a video signal. The preprocessor comprises: a correlated double sampling amplifier (30) for outputting signal information corresponding to a difference voltage between the black level in a feedthrough period of the solid state image pickup device and a signal level in a charge signal output period; and offset cancelling means (38) for applying an offset cancelling voltage for cancelling an offset voltage corresponding to the difference voltage between the black level and the signal level in a state where the solid state image pickup device is optically interrupted to the input terminal of the correlated double sampling amplifier. The correlated double sampling amplifier cancels out the offset voltage and the offset cancelling voltage as signal components of polarities opposite to each other.