Provided is an erroneous communication prevention device operable to prevent erroneous communication between an RFID tag installed in a vehicle and an RFID communication antenna disposed at a roadside. The erroneous communication prevention device includes an erroneous communication prevention antenna operable to transmit erroneous communication prevention electromagnetic waves toward an electromagnetic wave leakage monitoring region. The electromagnetic wave leakage monitoring region is outside an RFID communication region where the RFID tag performs valid communications with the RFID communication antenna. In addition, the electromagnetic wave leakage monitoring region is defined in a region where the RFID tag is enabled to perform communications using electromagnetic waves transmitted from the RFID communication antenna.