To provide a photodetector circuit capable of obtaining signals in different periods without being affected by characteristics of a photoelectric conversion element. The photodetector circuit has n signal output circuits (n is a natural number of 2 or more) connected to the photoelectric conversion element. Further, the n signal output circuits each include the following: a transistor whose gate potential varies in accordance with the amount of light entering the photoelectric conversion element; a first switching element which holds the gate potential of the transistor; and a second switching element which controls a signal output from the transistor. Thus, after data based on the amount of light entering the photoelectric conversion elements is held as the gate potentials of the transistors, the second switching elements are turned on, whereby signals in different periods can be obtained without being affected by characteristics of the photoelectric conversion element.