PURPOSE: To provide an automatic on-vehicle accident reporting device and the automatic accident reporting system which can be easily mounted on the vehicle and suppresses the generation of the inconvenience by the accident.

CONSTITUTION: An accerelation detection part 11 which detects the accerelation of the vehicle in the three-dimensional direction and a communication part 14 which sends the information on the accident including the position and accerelation of the vehicle and the time detected by a GPS receiver 2 when the detected accerelation is higher than the threshold value set in advance and which accepts the accident information which is processed for outputting voice which is sent from the center 4 are made as one unit. For example, when it is given at the entrance of the expressway, the automatic on-vehicle reporting device can be mounted on every vehicles which travel on the expressway. Thus, even when any vehicle meets an accident, reporting is available.