To provide a wrong determination prevention method of communications between road and vehicle capable of increasing surely the number of times when an instruction to a road side indicator of a road side wireless installation agrees with an instruction content to the driver of a vehicle having an on-vehicle equipment, and preventing wrong determination of the communications between the road and the vehicle.

Wrong instruction to the road side wireless installation 4 and to the driver of a vehicle having the on-vehicle equipment 8, 12 is prevented by using a finish monitoring timer 32 of the communications in a system for executing radio communication between the road side wireless installation 4 and on-vehicle equipment.