A solid-state image sensor includes a pixel array, and an analog to digital converter for converting a voltage signal read from the pixel array from analog to digital form, wherein the analog to digital converter includes a counter counting a first clock signal for a period depending on a voltage value of the voltage signal, and wherein a least significant bit of a count value of the counter is determined based on an exclusive OR of outputs of two 1-bit counters operating at a frequency of the first clock signal.