Signal charge that has accumulated in photodiodes of a photoreceptor area in a CCD is multiplied by a charge multiplier and then applied to a floating diffusion amplifier, which has been set to a small conversion coefficient, or to floating gate amplifier, which has been set to a large conversion coefficient. If the accumulated amount of signal charge is small, the charge is converted to a video signal by the floating gate amplifier having the large conversion coefficient. If the accumulated amount of signal charge is large, the charge is converted to a video signal by the floating diffusion amplifier having the small conversion coefficient. Thus a video signal having a high level is obtained even if the amount of signal charge is small. Since it is unnecessary to change driving pulses that are applied to the charge multiplier, the multiplication factor of the charge multiplier will not fluctuate.