In the present invention, second step is provided, carbon dioxide feeding mechanism (10) is by 2 minutes (predetermined) of driving, first time air circulation fan (31) stops therebetween, and the 2nd process of supply is executed after dispersion steps, carbon dioxide feeding mechanism (10) and air circulation fan (31) stop 2 minutes (scheduled second time), repeat interaction, if supply step or dispersion steps of the temperature (T) during agricultural house (AH) is at least execution of T2, driving circulating fan (31) is prohibited, until the following dispersion steps in the end at moment.
