ABNORMALITY DIAGNOSTIC SYSTEM FOR INTERIOR TELEPHONE WIRING AND ABNORMALITY DIAGNOSTIC UNIT AND DIAGNOSTIC SIGNAL RETURNING UNIT USED FOR THE SYSTEM

PROBLEM TO BE SOLVED: To quickly diagnose abnormality in interior telephone wiring with high accuracy. SOLUTION: An abnormality diagnostic system 1 is provided with change-over switches 2c and 3c which are installed to a plurality of branch terminals t of an indoor wiring section 6 and cut off the wiring section 6 between the terminals t from a telephone line as independent wiring 6a, an abnormality diagnostic unit 2, and a diagnostic signal returning unit 3. In a state where the independent wiring 6a is cut off from the telephone line by the switches 2c and 3c, the abnormality in the wiring 6a is diagnosed based on a diagnostic signal exchanged between the units 2 and 3.