In the car navigation system including a vehicle communication apparatus mounted on a vehicle, different diffusion codes are assigned to each road such as a single lane road and a road with double lanes. In data transmission to other vehicles, each vehicle switches to and uses the diffusion codes assigned to the road on which own vehicle currently travels. Even if many on-coming vehicles travel in line, radio wave interference between the vehicles does not occurs and the lacking of communication channels also does not occurs because each vehicle uses the diffusion codes assigned to the road on which own vehicle travels.