PURPOSE: To prevent the occurrence of dew condensation owing to draw-in of hot air having high humidity by providing air direction varying plates wherein the areas of each of the air inlet end surface parts of the adjoining air direction varying plates is lower than that of each of other air direction varying plates.

CONSTITUTION: A coupling beam 6 is coupled to a coupling shaft 7, located to the side of each air direction varying plate 1, through a coupling bearing hole 8, and a part of air direction varying plate 1 group is displaceable in parallel. Two coupling beams 6 are provided, and parallel displacement of two groups of upper and lower groups of the air direction varying plates 1 can be individually effected. End surfaces W on the inlet side of the adjoining central air direction varying plates 9 of the coupling beam 6 of each group are notched. Since the end surface of the air inlet of the central air direction varying plate 9 is notched, discharge air 10 flows along the central air direction varying plate 9, and since hot air having high humidity is not drawn in, dewing water can be prevented from a drip.