The invention provides a display unit that has a display area and first and second photodetectors 10a and 10b on a substrate and outputs as a light intensity signal S a light intensity detected by the first and second photodetectors 10a and 10b. The first photodetector 10a includes a first photodetection circuit LS1 outputting a first output signal Sa to an ambient light photosensor reader 20, and the second photodetector 10b includes a light-reducing unit and a second photodetection circuit LS2 outputting a second output signal Sb to an ambient light photosensor reader 20. The ambient light photosensor reader 20 includes a photodegradation factor calculator 21 calculating a photodegradation reparation factor K, a photodegradation rate calculator 22 deriving a photodegradation rate D based on the photodegradation reparation factor K, and a light signal output unit 24 outputting a light intensity signal S based on the photodegradation rate D.