PURPOSE: To discriminate a installed location of a terminal equipment comparatively easily.

CONSTITUTION: A master set and plural terminal equipments to which a specific address is respectively set are connected by a signal line. The master set specifies an address of each terminal equipment by using an address data of a transmission signal to access each terminal equipment individually. The terminal equipment returns a return signal to the master set for a return signal band of the transmission signal. The transmission distance up to each terminal equipment is calculated based on a delay (t) from the terminal equipment at a return signal band RSP with respect to a return start point of time of the return signal from the terminal equipment when each terminal equipment is individually accessed.