When a vehicle is located within a coverage of a radio station, a navigation system for the vehicle outputs audio guidance on the basis of received traffic information, provided that the traffic information is to be output under a predetermined audio output condition according to a congested area or stores the traffic information in a storage section, provided that the traffic information is not under the predetermined audio output condition according to the congested area. Then, when the vehicle is located out of the coverage of the radio station, the navigation for the vehicle outputs traffic information stored in a storage section as audio guidance.