A touch panel includes a plurality of pixels each of which is provided with a photo sensor including a photodiode, a first transistor, and a second transistor. Each pixel performs first operation in which a potential of a photodiode reset signal line which is electrically connected to the photodiode is set so that a forward bias is applied to the photodiode, second operation in which a potential of a gate of the first transistor is changed by a photocurrent of the photodiode, and third operation in which a potential of a gate of the second transistor is changed and the photo sensor output signal line and a photo sensor reference signal line are brought into conduction through the first transistor and the second transistor so that the potential of the photo sensor output signal line is changed in accordance with the photocurrent.