A hazardous behavior determining unit (3) determines a vehicle that is conducting or is likely to conduct hazardous driving from among one or more vehicles around a host vehicle and a type of the hazardous driving using information indicating states of the host vehicle and the vehicles and a surrounding situation and behavior information stored in an onboard database (2). A registered vehicle identifying unit (5) identifies a vehicle that corresponds to hazardous vehicle information stored in the onboard database (2) by collating numbers of a license plate detected by a number detecting unit (4) with numbers stored in the onboard database (2). A hazard predicting unit (6) predicts a risk to the host vehicle using the determination result from the hazardous behavior determining unit (3) and the identification result from the registered vehicle identifying unit (5).