An automatic driving system mounted on a vehicle includes a navigation device that searches for a route from a current position of the vehicle to a destination, a high precision map unit that generates detail information of the route based on the searched route and map information, and an automatic driving control device that performs automatic control of acceleration and deceleration and steering of the vehicle using at least the detail information. The high precision map unit divides the route into a plurality of block regions and, out of the detail information corresponding to the block regions, outputs the detail information currently required for the automatic control to the automatic driving control device in a unit of block region.