A driving assistance device includes a housing, a controller, a plug connector, and a power line. The controller is received in the housing and includes a microprocessor, a supply line, a signal line, and a storage module. The storage module is electrically coupled to the microprocessor. The plug connector is assembled within the housing, and electrically coupled to the microprocessor via the supply line and the signal line. The power line is electrically coupled to the supply line. The present disclosure further discloses a driving assistance system and a vehicle employing the driving assistance device.