To provide a navigator having a security function with a burglar prevention effect improved.

An L vehicle 460 repeats receiving information from a K vehicle 450 to be a transmitter vehicle. Thus, abnormality occurring to the K vehicle 450 is monitored. Also, the L vehicle 460 repeats transmitting information to an I vehicle 430 to be a transmission destination vehicle in parallel to information reception from the K vehicle 450. Thus, abnormality occurring to the L vehicle 460 is monitored by the I vehicle 430. That is, each vehicle monitors abnormality occurring to the transmitter vehicle and has the transmission destination vehicle monitor abnormality occurring to its own vehicle. When information reception from the K vehicle 450 stops, the L vehicle 460 performs processing during the abnormality on the ground that abnormality has occurred to the K vehicle 450.