PURPOSE: To eliminate an incredible sense of a telephone set user by informing a busy line state to the telephone set when an emergency notice equipment detects it that a general telephone set is going to use a telephone line while the equipment is busy through the line.

CONSTITUTION: When an emergency notice equipment enters the notice operation, a relay 1 is connected to a transmission/reception circuit 2, which implements data transmission reception. A relay 4 is connected to a telephone set busy state discrimination circuit 3 together with the operation to monitor the state of a hook switch 5. When the state change in a subscriber's equipment 5 is detected through the hook-off of a handset to use the subscriber's equipment, a relay 6 is connected to a message transmission circuit 7, a receiver is connected by the circuit 7 and the circuit 7 sends a message of a busy state of the emergency notice equipment or the line to the receiver.