A roadside radio device includes a first radio unit which receives a radio data packet from an in-vehicle radio device, and a first application unit which processes application data. The first radio unit includes a radio data processing unit including a correlation processing unit which compares a data string of vehicle identification information with a data string of communication type information to determine whether there is a correlation in the radio data packet. When the correlation processing unit determines that there is the correlation in the radio data packet, the first radio unit outputs the application data included in the radio data packet to the first application unit. When the correlation processing unit determines that there is no correlation in the radio data packet, the first radio unit treats the radio data packet as invalid data.