A row scanner selects an arbitrary row in an pixel array unit. Per-column AD converters separately convert voltage signals respectively outputted from a column of a plurality of unit pixels in the selected arbitrary row into digital signals. A column scanner sequentially outputs the digital signals by a column-scanning operation thereof. An AD conversion result adjuster judges whether or not the digital signals reach a predetermined judgment value or the status equivalent to the digital signals reaching the predetermined judgment value is generated, and fixes the digital signals to digital pixel values set in accordance with the predetermined judgment value when a result of the judgment is positive.