Abstract: Provided is a display device using a TFT serving as a switching element, in which image deterioration of the display device is prevented by suppressing a photo leakage current to be small, and in particular, in which a density of defects which become positive fixed charges by light present in a protective insulating film of the TFT is defined to suppress the photo leakage current. In the display device using the TFT, the TFT includes an insulating film, an amorphous silicon film, a drain electrode and a source electrode, and a protective insulating film laminated on a gate electrode covering a part of a surface of an insulating substrate in the stated order, in which the protective insulating film includes a defect which becomes a positive fixed charge under light irradiation. A surface density of the defects is preferably 2.5×1010 cm?2 or more to 4.0×1010 cm?2 or less.