A protective mechanism terminates the emission of a laser beam from an inadvertently inverted laser input device. A transmitting/detecting circuit is positioned under a laser input device that emits laser beams from a laser light. The transmitting/detecting circuit projects an infrared ray to a working surface to be reflected therefrom, with the reflected infrared ray detected by the transmitting/detecting circuit. The laser light is turned off if the transmitting/detecting circuit fails to detect the reflected infrared ray.