PURPOSE: To transmit quickly fire information by allowing a control unit to collect the presence of lots of call request signals.

CONSTITUTION: A control unit 10 calls a power supply unit 20, a display operation unit 30, a fire detection unit 40 and a relay unit 50 sequentially and circulatingly through a data line DL to control transmission reception of various information or the like. When a fire sensor senses the breakout of a fire and transmits a fire signal to the unit 40, an MPU 41 transmits a call request signal to the unit 10 via a call request signal line CL to detect a call signal. The unit 10 sends the address of the unit 20 and a state information return instruction immediately through the line DL and awaits the return of the information of the unit 20, receives return state information and conducts the operations above to each of the units 30, 40, 50. Even when the number of the units controlled by the control unit is increased, fire information is quickly transmitted to the control unit.