The present invention is to provide a rapidly rechargeable warning device, which includes a power receiving element for receiving external electric power, a charging control module for receiving electric power from the power receiving element, a fast energy storage element (e.g., a supercapacitor or any rapidly rechargeable components) being rapidly charged by the charging control module and then outputting electricity stored therein, an warning element (e.g., a light-emitting diode, a buzzer, or a vibrator) capable of issuing a warning signal (e.g., a light signal, a warning sound, or vibrations) upon receiving the electricity outputted by the fast energy storage element. Thus, since the fast energy storage element can be fully charged within a short time through being connected to a cigarette lighter socket of a car, or a transformer connected to an indoor power source, the warning device can be used immediately and effectively prevent user from using one-time batteries.