PURPOSE: To realize a curved road alarm device to give an alarm to danerous car speed by finding a radius of curvature of a curved road without finding the radius of curvature of the curved road from a white line coordinate in a two-dimensional picture image and without setting a transmitter on the curved road.
CONSTITUTION: A radius of curvature of a curved road is detected by collating a letter pattern decided by way of applying binarization treatment and edge treatment to a picture image signal obtained from a two-dimensional camera 1 to pick up an image of a curve curvature display sign set on a curved road and a letter pattern of a previously memorized curve curvature, standard allowed car speed previously memorized is found from this radius of curvature, and when current car speed 2 is higher than allowed car speed multiplying the standard allowed car speed with a correction coefficient corresponding to a previously memorized vehicle surrounding circumstance, it is judged as over speed and an alarm is energized for a specified period of time.