To effectively utilize the water for humidification utilized on heating as a fire fighting water by opening a valve on detecting a fire in a room and by introducing the water for humidification supplying to a piping for humidifica tion to a branched piping and by dispersing the water by using a sprinkler to extinguish.

When a fire in a room is detected by a controlling unit comprising a processing unit 11 for supplying a switching control signal to a valve 9 through an instrumentation line 12 and a thermistor 4 of an air conditioner 2 for supplying temperature information to the processing unit 11 through the instrumentation line 12, the valve 9 is opened, the water for humidification in a water supply piping for humidification 7 upstream a valve 6 is introduced to a branched piping 8 and dispersed by a dispersing head 10a through the valve 9 to extinguish. By this constitution, the water for humidification to be used only for heating can be effectively utilized for fire extinguishing and results in lowering the investment cost.