PURPOSE: To detect the mis-setting of a terminal equipment or a setting mistake of a transmission address and to discriminate the location of a terminal equipment in the mis-setting state.

CONSTITUTION: The system consists of a mis-setting terminal detector 1 provided with a polling means 10 and a deciding means 11 and of each terminal equipment and each terminal equipment is provided with a connector address setting means 22 and a terminal address setting means 21. The deciding means 11 compares the combined pattern of three addresses as a terminal address obtained from each terminal, a connector address at polling, and a transmission terminal address designated at polling with a correct combination pattern 11a stored in advance, decides the installation mistake of each terminal equipment and the transmission address setting mistake state and discriminates the location of the terminal equipment from the connector address.