A route information supply system comprises a reception module which receives information on a current position and a destination from a terminal device by communication, a map data storage module storing at least detailed map data and summary map data, a traffic information storage module which stores traffic information, a route search module which searches for a guidance route based on the current position and the destination, a map information generation module which generates map information on an area containing the searched route by use of the map data storage module, and an output module which outputs the generated map information to the terminal device. When an event satisfying a prescribed condition regarding the traffic information exists in the area, the map information generation module generates map information on an area in the vicinity of a point where the event has occurred by use of the detailed map data.