PURPOSE: To enable a maintainer to execute a test for a junction line of alarm signal without consuming a large amount of time and labor, by providing a relay which works by a test operation given from a specific station and sends back an artificial alarm signal at each slave station.

CONSTITUTION: A relay R for generation of artificial alarm signal is provided to each of slave stations 1-1∼1-n and connected to each of test keys C1∼Cn provided in response to the stations 1-1∼1-n, respectively. A maintainer resident at a maintenance concentrated station 3 operates the key C1 for test of alarm signal junction lines 2-11∼2-1m. Thus an earth is connected to a test junction line 4-1, and a test signal ck1 is transferred to the station 1-1. Then the relay R works at the slave station to connect the earth to all junction lines 2-11∼2-1m via a contact (r). As a result, artificial alarm signals al11∼al1m are sent back to the station 3 via the junction lines 1-1∼1-1m. Thus alarm lamps L11∼L1m glow at the station 3 to confirm the normalness.