Thin film transistors including an oxide semiconductor containing indium, gallium, and zinc are easily arranged in a matrix over a large substrate and have small characteristic variations. With amplifier circuits and driver circuits of display elements which include the thin film transistors including an oxide semiconductor containing indium, gallium, and zinc with small characteristic variations, intensity distribution of light received by the photodiodes arranged in a matrix is converted into electrical signals with high reproducibility and output, and the display elements arranged in a matrix can be uniformly driven.