Two gate electrodes are provided on upper and lower sides of an oxide semiconductor active layer through respective insulating films. In addition, a first read-out electrode and a second read-out electrode are provided on right and left sides of the oxide semiconductor active layer. In the optical sensor element, in a case where a voltage is applied to each gate electrode, a potential difference occurs between the first read-out electrode and the second read-out electrode, and intensity of irradiation light is detected based on a current that flows between the read-out electrodes.