A road-vehicle communication system includes an in-vehicle communication apparatus and a roadside communication apparatus, the in-vehicle communication apparatus has a vehicle information transmission unit that transmits vehicle information related to a vehicle. The roadside communication apparatus has a storage unit storing a plurality of pieces of data to be transmitted to the in-vehicle communication apparatus. A vehicle information reception unit receives vehicle information transmitted from the in-vehicle communication apparatus. A transmission data generation unit combines a plurality of pieces of data stored in the storage unit to generate a single piece of transmission data. A data transmission unit transmits the data generated by the transmission data generation unit to the in-vehicle communication apparatus. A combined number adjustment unit adjusts the number of pieces of data to be combined by the transmission data generation unit, based on vehicle information received by the vehicle information reception unit.