PURPOSE: To provide a system for facilitating the indoor wiring of a unit housing through a hierarchic working system in which the minimum necessary illumination is ensured by lighting an emergency lamp E even if the lamp is unlighted immediately upon tripping of branch circuit breaker in a main distribution board and the circuit can be recovered from that room.

CONSTITUTION: A trip signal inputted to a master unit 7a is delivered on a signal line 9a to a slave unit through the use of a branch circuit breaker B1-B4 provided with an alarm switch. An emergency lamp E is lighted by a power supply superposed on the signal 9a and the circuit is recovered by operating a recovery switch disposed closely to the emergency lamp.