A flashing device for a vehicle includes a power filtering unit connected to a power source for outputting a negative voltage after filtration, a detecting unit for detecting the negative voltage from the power filtering unit, an oscillating unit electrically connected to the detecting unit, and a drive unit electrically connected to the detecting unit and the oscillating unit. The oscillating unit generates a flashing signal when the detecting unit detects the negative voltage. The drive unit receives the flashing signal and causes the flashing device to flash.