Wheel assembly identification indicating members and first communication devices are respectively mounted to wheel assemblies mounted to a vehicle body. The indicating members have characteristic appearances, which are different among the wheel assemblies and which make the respective wheel assemblies identifiable in external appearance. The first communication devices transmit by wireless transmission pieces of wheel assembly information on the respective wheel assemblies as well as pieces of identification information held by the respective first communication devices. A second communication device provide on the vehicle body side receives the pieces of wheel assembly information and the pieces of identification information and specifies the respective wheel assemblies from which the pieces of wheel assembly information are transmitted, by referring to a correlation between prestored piece of information on characteristic appearances of the indicating members and the pieces of identification information.