To provide a proper information as to countermeasures consequent on the state change of a road face, for example, a timing for attaching/ detaching a tire chain, etc.

A navigation ECU 10 judges necessity for a tire chain based on a temperature detected by an environment sensor 16, snow information on road faces obtained by a communications device 22, etc. When the attachment or detachment of the tire chain is judged to be necessary, an attachment/ detachment place is searched for on the basis of data of a map database 14 and an instruction to attach/detach the tire chain at the obtained place is output.