To provide a large-area sensor capable of converting light intensity distribution received by photoelectric conversion elements disposed in a matrix into electrical signals with high reproducibility and extracting them, and to provide a display device that is mounted with the area sensor and has a high writing speed and little display unevenness.

Thin-film transistors employing an oxide semiconductor containing indium, gallium, and zinc are easily disposed on a large-area substrate in a matrix and have small characteristic variations. An amplifier circuit and a drive circuit of display elements, which are constituted of the thin-film transistors employing the oxide semiconductor containing indium, gallium, and zinc and have small characteristic variations, are used to convert light intensity distribution received by the photodiodes disposed in a matrix into electrical signals with high reproducibility for extraction, thus the display elements disposed in a matrix being driven in a uniform manner.

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