When searching of a location of a vehicle is commanded, a vehicle search signal is transmitted from a portable device. The vehicle search signal includes an ID code of the portable device. When a vehicle side communication unit receives the valid ID code, the vehicle side communication unit transmits a vehicle side response signal to the portable device. The portable device computes a distance from the portable device to the vehicle based on a signal level of the received vehicle side response signal. A notifying device notifies the computed distance.