A solid-state image sensor where dark current components fluctuating due to temperature changes are removed from pixel signals without reducing resolution during AD conversion. The sensor has a DA converter for generating a reference signal that increases at a constant slope from a predetermined initial signal level, a comparator for comparing the reference signal with a pixel signal, a counter for performing a counting operation in synchronization with increase in the reference signal, a latch circuit for holding as a quantized value of the pixel signal a discrete value at the time when the reference signal and the pixel signal coincide with each other, an average calculator for calculating an average of the quantized values of pixel signals read out from plural light-shielded pixels, and a reference signal adjuster for setting based on the average the initial signal level of the reference signal compared with the pixel signal read out from a light-receiving pixel.