A lightning strike alarm system using a Bipolar Conventional Air Terminal comprises a sensor electrically connected to a rod element electrified by a ground charge and an electrification plate-cone or an electrification plate-tube electrified by a thunderstorm cloud, and configured to measure electric energy induced in the electrification plate-cone or the electrification plate-tube; and a controller configured to determine that the thunderstorm cloud has approached when the electrical energy is greater than a reference energy; and an alarm device configured to output an alarm signal, based on a result of determining that the thunderstorm cloud has approached, wherein the sensor comprises: a luminescence unit, including a voltage stabilizer preventing induction of a high voltage due to the thunderstorm cloud, configured to emit light by the electric energy; and a light receiver configured to receive the light, convert the light to electric energy, and transfer the electric energy to the controller.