The present invention inspects a defect of a photo sensor element or a photo sensor line. A display device includes a substrate, a plurality of pixels formed on a display region of the substrate, and a plurality of video lines for applying a video voltage to the plurality of pixels. The substrate includes at least one photo sensor element which is formed on a region outside the display region, a photo sensor line which is connected with at least one photo sensor element, and at least one first switching element which connects at least one photo sensor element and at least one video line out of the plurality of video lines. At the time of inspecting the photo sensor element, the first switching element is turned on and, at the same time, a predetermined inspection voltage is applied to at least one photo sensor element via the photo sensor line thus applying a signal to the pixel via the first switching element and the video line, and in response to a turn-on state of the pixel at the time of applying the signal to the pixel, a defect of at least one of at least one photo sensor element and the photo sensor line can be detected.