The airflow controlling device includes a bacteria counting portion counting bacteria of a controlled space a first smoothing processing portion performing a first smoothing process on the bacteria count a second smoothing processing portion performing a second smoothing process on the bacteria count a bacteria reducing capability storing portion storing a bacteria reducing capability relative to each flow rate a first flow rate evaluating portion selecting a flow rate matching a bacteria reducing capability compatible with an increase in a bacteria count forecasted from the processing result of the first smoothing processing portion a second flow rate evaluating portion selecting a flow rate matching a bacteria reducing capability compatible with an increase in a bacteria count forecasted from the processing result of the second smoothing processing portion and a flow rate determining portion selecting a flow rate into the controlled space based on the flow rates selected by the first and second flow rate evaluating portions.
