A radio resource allocation system in which equipment placed on a road allocates a radio resource to in-vehicle equipment that exists in a given area is provided. The radio resource allocation system includes the in-vehicle equipment mounted on a vehicle that communicates with another in-vehicle equipment by using the radio resource. The in-vehicle equipment includes a signal transmitting unit that transmits a signal showing that the own vehicle exists in the given area. The roadside equipment includes a radio resource allocation unit that allocates the radio resource to the in-vehicle equipment when the roadside equipment receives the signal transmitted by the signal transmitting unit, and a radio resource release unit that releases the radio resource when the roadside equipment does not receive the signal from the in-vehicle equipment that is allocated the radio resource by the radio resource allocation unit.