To provide a technique for identifying an apparatus generating an interference wave exists inside a vehicle or outside a vehicle, without need of antennas to be provided both inside and outside the vehicle cabin.

An interference wave source discrimination device determines whether an interference wave is received at a predetermined channel (step 130). When the interference wave reception is determined, if a variation amount of reception intensity at the channel is smaller than a first reference value, the interference wave source discrimination device determines that the interference wave generation apparatus exists within the vehicle cabin, whereas if a variation amount of reception intensity at the channel exceeds a second reference value, determines that the interference wave generation apparatus exists outside the vehicle (step 140).