To solve the problem that it is difficult for a person who does not have the detailed knowledge of automobiles to properly judge when a tire should be replaced by viewing the abrasion state of the tire, and a method for measuring the depth of a groove is troublesome in terms of its inspection itself and may easily be forgotten.

Mileage that is calculated according to the speed of a tire is compared with distance that is calculated by a parameter independent of the speed of the tire. When the difference reaches a fixed value, it is judged that the tire is worn out. The abrasion state of the tire is objectively judged by a numerical value for automatic reporting, thus letting a driver know when the tire should be replaced without any inspection by the driver. In the report, exclusive narrow-area communication is used, the state of an automobile is reported with a case where the automobile enters a service station as a trigger. Additionally, even if the size is changed when a GPS is used to replace a tire by a new one, this situation can be coped with without changing the setting.