An analog voltage signal corresponding to a light intensity received by a photosensitive pixel is sampled. At the time when thus sampled analog voltage signal is inputted into a clamping circuit, a comparative voltage signal changing over time is coupled therewith by means of capacitive coupling. In a comparator circuit, the voltage level of the output signal from the clamping circuit is compared with the reference voltage level, while being changed. Then, the counter digital signal at the moment when the comparison result signal changes is latched in a holding circuit. Thus, imaging is executed accurately at a high speed.