An imaging device with excellent imaging performance is provided. The imaging device has a first circuit including a first photoelectric conversion element and a second circuit including a second photoelectric conversion element. The second circuit is shielded from light. In the imaging device, a current mirror circuit in which a transistor connected to the second photoelectric conversion element serves as an input transistor and a transistor connected to the first photoelectric conversion element serves as an output transistor is formed. With such a configuration, the amount of photocurrent in the first circuit from which the contribution of the dark current of the first photoelectric conversion element has been excluded can be detected.