PURPOSE: To reproduce a picture signal only by providing a flat portion to an output signal of an image sensor, sampling/holding two portions, the flat portion and a picture signal portion, and generating and clamping a pulse amplitude modulated signal proportional to the picture signal.

CONSTITUTION: The phase of a pulse timing of a reset pulse RS driving the CCD image sensor 12 is advanced and the flat portion as a reference level is provided in an output signal of the sensor 12. Then two portions, the flat portion and the picture signal portion are sampled and held (19) during one picture element period to generate a pulse amplitude modulation signal PAM having an amplitude proportional to the picture signal. The signal PAM is clamped (26) and fed to one input of an A/D converter 29, a data strobe pulse ST is fed to the other input and the center portion of the picture signal is extracted. The extracted signal is outputted while being quantized. Thus, a DC bias voltage and a leakage signal of a reset pulse are eliminated surely.