An active matrix substrate including an external signal supplying circuit for externally supplying the video signals to the data lines. The external signal supplying circuit includes a data line connection section connected to the data lines; an inspection signal inputting section and an inspection signal outputting section both connected to the data line connection section; and a switching device for electrically connecting the inspection signal inputting section or the inspection signal outputting section to the data line connection section. After the active matrix substrate is subjected to an electrical inspection, a short ring is formed for electrically connecting an inspection signal inputting terminal provided with an inspection signal inputting section, an inspection signal outputting terminal provided with an inspection signal outputting section, a first terminal provided with a gate driving circuit, a second terminal provided with a source driving circuit, and the data line connection section, in a case when the active matrix substrate is judged to have no defect; and then the short ring is removed after an alignment treatment of a display medium.