PURPOSE: To decide a travel direction in many directions and detect a position by receiving a radio wave sent from a sign post radio part by an on-vehicle reception part and knowing the position and travel direction of a vehicle from the display signal of a comparing circuit.

CONSTITUTION: The output of a phase comparing circuit 12 is as shown in a figure. Namely, when the vehicle travels to a sign post position P from the south and enters a range wherein the radio wave from the sign post can be received, a phase comparing circuit 12 outputs the display signal indicating that the phase is θ1. When the vehicle enters an intersection and turns to the east, namely, nearby the sign post position P, the phase comparing circuit 12 outputs the display signal indicating that the phase is θ2 continuously until the vehicle exist the receivable range. It is discriminated that the vehicle passes right below the sign post position by entering the range from the south and turns to the east from the change of the display signal.