PURPOSE: To enable the serial transmission of the control signal related to safety by setting the earthquake control information at AUTO after abnormality of the transmission has continued for a predetermined time, and holding the earthquake control information just before abnormality is generated in the other case.

CONSTITUTION: Normality and abnormality of the serial transmission is judged, and in the case of YES, the transmission receiving data such as the earthquake control operation command or the like is input to be stored in a read-write possible memory (RAM) 13, and in the case of NO, since a possibility of generation of the instant noise exists, a judgement that abnormality of the transmission is continued more than the predetermined time or not is performed, and in the case of YES, disconnection of a serial transmitting wire 7 or fault of a transmitting device 2 is judged, and in the case of NO, since abnormality of the serial transmission to be caused by the noise or the like is judged instantly and the transmission progresses to an outlet, the condition just before abnormality of the transmission is generated is held. Furthermore, OFF or not of the earthquake control information on the RAM 13 is judged, and in the case of YES, the earthquake control information is set at AUTO, and in the case of NO, the condition just before abnormality of the transmission is generated is held to process the fire control information or the like, and the transmission progresses to the outlet.