To enable a user to easily and certainly select and set a desired detour in setting the detour for detouring around a traffic congestion in a navigation system.

When a detector 31 of a traffic congestion on a guidance route detects a traffic congestion on the guidance route forward in the travel direction based on information in a VICS information input section 14, a detour distance display section 33 for selection input displays a detouring distance such as "2km", "5km", "10 km". When the user intends to select "5km", for example, a detouring distance map display section 34 for selection input displays the 5km point on the guidance route. When the user looks at it and judges that it does not sufficiently detour around the traffic congestion, the user selects the detouring such as "10 km". When the user judges that this distance is sufficient, a detouring route calculation section 39 calculates a detour. When the user recognizes this, it guides the user to this detour as a guidance route henceforth. All selected distance positions may be displayed on the guidance route.