An apparatus is disclosed for detecting error in a transfer system for transferring a substrate loaded upon fabricating of a liquid crystal display device of a flat panel display device. In an apparatus for detecting error of the transfer system, a test substrate includes reflective marks arranged symmetrically on both sides. An emitter generates light to radiate onto the transferring test substrate. A receiver receives light reflected from the reflective marks of the test substrate. A controller detects any error of the transfer system on the basis of the reflective times received by the receiver. A display displays any errors in the transfer system detected by the controller.