A method of repairing a defective one of devices mounted on substrate is provided. Devices are arrayed on a substrate and electrically connected to wiring lines connected to a drive circuit, to be thus mounted on the substrate. The devices mounted on the substrate are then subjected to an emission test. If a defective device is detected in this test, a repair device is mounted at a position corresponding to a position of the defective device. At this time, after wiring lines connected to the defective device are cut off, the repair device is electrically connected to portions of the wiring lines, the portions of the wiring lines being located at positions nearer to the drive circuit side than the cut-off positions of the wiring lines. Since a defective device is repaired by a simple step that is carried out by simply mounting and fixing a repair device without removal of the defective device, it is possible to eliminate the need for any complicated, microscopic work; for example, removal of the mounted devices, and/or selective removal or repair of an insulating layer.