An apparatus for detecting error of a transfer system that is adapted for detecting an error of a transfer system transferring a substrate loaded upon fabricating of a flat panel display device in a real time is disclosed. In the apparatus, an emitter generates a light and radiates the light into a transfer system. A receiver receives light reflected from the transfer system. A controller controls light radiation from the emitter, and measures the time such that a reflective light of the transfer system is received from an emitting point of the emitter to the receiver. The controller also detects a displacement of the transfer system using the measured time, a designated reference distance and a reference time. A display displays the displacement of the transfer system detected by the controller.
