US Patent 7734415 Navigation system

When a vehicle deviates from a guide route at a first branch point, the state of the first branch point is memorized. Afterward, when a second branch point becomes a target for a route guide and the state of the second branch point is similar to the memorized state, a user of the vehicle is provided with a guide for preventing deviation from the guide route at the second branch point with a manner of the guide changed. This procedure allows learning of tendency of the user with respect to a state apt to cause the user to mistake a guide route. A guide to help prevent a user from deviating from a guide route at a branch point can be thus performed appropriately.