The reading accuracy of an imaging device is increased. Clear image capturing is performed even in the case where the luminance is high. A reading circuit of the imaging device includes an amplifier portion and a conversion portion. The amplifier portion amplifies a potential difference between a first signal and a second signal that are sequentially input and outputs the amplified difference to the conversion portion. The conversion portion converts the output potential of the amplifier portion into a digital value. The amplifier portion is reset on the basis of a first reference potential and the first signal and amplifies the potential difference on the basis of a second reference potential that is different from the first reference potential and the second signal.