PURPOSE: To supply sir where the fluctuation range of temperature and humidity is precisely controlled in a fine range of specific % RH respectively.

CONSTITUTION: The open air 1 is dehumidified by means of a dehumidifier 2 and temperature-controlled by means of a cooler 4 or a heater 5 as well. This temperature- controlled air is humidified by means of a quick humidification response humidification device 6 under control. This humidified air 7 is supplied. A reference 11 and a heater 5 are actuated by the indication of a temperature indication controller 10 which measures the supply air 7 by means of a temperature. The refrigerant is fed to the cooler 4 by the operation of the refrigerator 11 while the supply air is measured by a humidity sensor 12 and the quick humidification response humidification device 6 is operated by the indication of the humidity indication controller 13. It is necessary to operate the quick himudification response humidification device 6 promptly and accurately by the indication of the humidity indication controller 13. Therefore, some mm thick water layer should preferably cover the top of a horizontal plate-like heating medium in a stabilized manner so as to promtly respond to the intermission of the power source for the plate-like heating medium and heat and evaporate water intermittently.