PURPOSE: To purify a liquid pressure network in humidifying and purifying region by saturating the air with moisture exhibiting disinfecting action obtained from a solution in the humidifying and purifying region of air thereby disinfecting the air.

CONSTITUTION: An aqueous solution containing a treating agent exhibiting disinfecting action is sprayed to the water supply circuit of a humidifying means in the humidifying and purifying region. The humidifying and purifying region is connected, in the sense of liquid pressure, with a supply unit 35 disposed between a water outlet 36 communicating with a water distribution network and the liquid pressure inlet 20 of the humidifying means. An atomizing lamp 24 of a humidifier 23 has a plurality of nozzles 25 for blowing a jet of atomizing water into the air circulating through the system. According to the arrangement, the air circulating through the system is disinfected and scaling is reduced in the water of the air conditioning system and a steam circuit.