PURPOSE: To provide an inter-road/vehicle radio communication system in which inter-road/vehicle bidirectional information communication with high quality can be performed by a simplified, miniaturized, and low-cost equipment.

CONSTITUTION: This system is a radio communication system equipped with a road machine installed on a road and an on-vehicle machine provided at the vehicle and which performs communication between the road machine and the on-vehicle machine, and it is equipped with a carrier oscillator 25 provided at the road machine (a) and which supplies an unmodulated wave in communication from the road machine (a) to the on-vehicle machine (b) and in the communication from the on-vehicle machine (b) to the road machine (a), and a transmission modulator 28 arranged at the on-vehicle machine (b), and which modulates the unmodulated wave supplied from the carrier oscillator 25 in the communication from the on-vehicle machine (b) to the road machine (a).