PURPOSE: To simply check a signal path for any line connection only in its own equipment by using a loop comprising 1st and 2nd communication equipments and two transmission/reception transmission lines so as to check the signal path by line setting.

CONSTITUTION: A code generating section 120 in a 1st communication equipment generates a check code and it is outputted to a code insertion section 100 and a comparison section 130. The insert section 100 inserts the code to an input master signal and sends it to an outgoing transmission line. A code detection section 150 of a 2nd communication equipment detects a code in the master signal from a transmission line, the detected code is inserted to the master signal inputted to the 2nd communication equipment and sends the result to the incoming transmission line. The detection section 150 of the 1st communication equipment detects a code in the master signal of an incoming transmission line and sends it to a comparator section 130. The comparator section 130 compares a code from the incoming transmission line with a code from the generating section 120 and discriminates it that the signal path is established when they are coincident with each other. Thus, the signal path is simply checked only in its own equipment.