A vehicle on-board unit comprises a short range wireless broadcasting section, a vehicle identifier receiving section, a vehicle identifier counting section and a communication congestion determining section. The short range wireless broadcasting section is configured to broadcast a host vehicle identifier of a host vehicle equipped with the vehicle on-board unit. The vehicle identifier receiving section is configured to receive neighboring vehicle identifiers relating to neighboring vehicles located within a prescribed communication region around the host vehicle. The vehicle identifier counting section is configured to determine a number of the neighboring vehicle identifiers received by the vehicle identifier receiving section within a prescribed period of time. The communication congestion determining section is configured to determine a congestion condition of short range wireless communications within the prescribed communication region based on the number of the neighboring vehicle identifiers determined in the vehicle identifier counting section.