An organic light-emitting display device includes a first substrate and a second substrate; an organic light-emitting device disposed between the first and second substrates and includes a pixel electrode separately formed in each pixel, a common electrode, and an organic light-emitting layer disposed between the pixel electrode and the common electrode; and an electrode unit and at least one wiring unit that are disposed between the first substrate and the second substrate, the electrode unit including at least one thin-film transistor for transmitting a light-emitting signal to the pixel electrode and at least one capacitor, wherein an optical property modification layer obtained by modifying an optical property of at least one of the electrode unit and the wiring unit is formed on a surface of the at least one of the electrode unit and the wiring unit.