A solid-state image-pickup device having a plurality of analog-to-digital converters that has a plurality of pixels converting an incident-light quantity into an electrical signal and that converts an analog signal obtained from each of the pixels into a digital signal is provided. The analog-to-digital converter includes a plurality of comparators, wherein each of the comparators compares a reference voltage changing over time to the analog signal and wherein different reference voltages are transmitted to the comparators, and at least one counter that counts a time period required to finish the comparison made by the comparator, that stores information about a result of the counting, and that has different count numbers.