A navigation system comprising an apparatus and method for navigating a vehicle along a detour route when appropriate. A destination is set, and the current location, or site, is detected. Guiding is performed along an optimum route from the current location to the destination. When a traffic obstacle that requires a detour from the optimum route is detected, a detour to the destination that detours the traffic obstacle is searched. The detour is a route having the shortest time and/or the shortest distance from the current location to the destination. Guiding is performed for the detour route at a site located a prescribed distance from a branching point where branching is to be made from the optimum route to one of at least two detour routes.