To preliminarily prevent the illegal use of an on-vehicle responder set inside a vehicle by making it possible to automatically discriminate the illegal replacement of the on-vehicle responder.

An electronic module 4 recorded with an information signal A including a license registration number is set on a license plate 2, and an ETC on-vehicle 7 set inside the vehicle is recorded with an information signal B including a license registration number. Then, the information signals A and B obtained through roadside equipment 6 set at the gates of the entrance or exit of the road are automatically compared with each other, and when the license registration numbers are coincident, it is decided that the on-vehicle equipment is normally used, and the on-vehicle equipment is allowed to execute normal settlement processing. When they are not coincident, it is decided that the on-vehicle equipment is illegally used, and an instruction to stop the settlement processing is issued.