A liquid crystal display device having high quality and high reliability is manufactured by preventing the occurrence of damages on a terminal portion due to the radiation of laser beams in cutting a substrate of the display device which is formed using a plastic substrate by the radiation of laser beams. A first substrate has a cutting line at a position which faces a terminal portion of a second substrate. In cutting the first substrate along the cutting line, laser beams are radiated to the first substrate along the cutting line so as to form a groove having a predetermined depth in the first substrate. Then, a load is applied to the first substrate along the groove so as to cut the first substrate.