Tire-side transmitters, attached to respective tires, have inherent ID numbers. On-vehicle receivers, disposed on an automotive vehicle, receive signals containing ID numbers. A control unit, disposed on the automotive vehicle, can identify tire mounting positions of respective tires based on the signals containing ID numbers received by the on-vehicle receivers. The controlling means memorizes information related to tire mounting positions of respective tires. Furthermore, the controlling means causes a displaying means disposed on the automotive vehicle to inform an automobile user of information relating to tire rotation, such as appropriate shifting directions instructing desirable tire mounting positions for respective tires, when predetermined tire rotation timing has come.