To provide a navigation system for guiding so as to smoothly perform turning to the right or to the left at intersections.

The navigation system comprises: an acquiring means of the number of right-turn and left-turn lanes for acquiring the number of right-turn and left-turn lanes for turning to the right or the left at intersections; and an approaching lane information acquiring means for acquiring the number of approaching lanes after turning to the right or the left. The navigation system also has a driving lane acquiring means for acquiring a lane in which a vehicle is running, and then by a lane changing judging means from these information, the need of changing the lane is decided by comparing the driving lane with an approaching lane to be approached. When the need of changing the lane is decided by the lane-changing deciding means, a lane-changing guiding means guides the change of the driving lane.