A display device includes a display element, a thin-film transistor for controlling light emission from the display element, and a signal line connected to the thin-film transistor. The thin-film transistor includes a gate electrode formed on an insulating substrate, a gate insulating film formed on the substrate so as to cover the gate electrode, a channel layer formed on the gate insulating film, and a source electrode and a drain electrode connected to the channel layer. A mounting terminal part of the signal line is formed by laminating a metal oxide layer on a copper layer; its cross section is trapezoidal; and the side surface and the periphery of the top surface of the mounting terminal part are covered with a protective film.