A TFT panel is manufactured by a process of forming an oxide voltage-apply lines, gate lines, and capacitor lines on an insulating substrate, and a process of forming thin-film transistors, pixel electrodes, data lines, and ground lines. In a state that one end of the gate line and both ends of the capacitor line are connected to the oxide voltage-apply line, oxide films are formed on the surfaces of the gate line and the capacitor line by anodization. After forming the oxide film, the gate line and the capacitor line are electrically separated from the oxide voltage-apply line.