Abstract: Peripheral ribs 34A, 34B of a damper plate 30 are raised from at least two sides along an extending direction of a rotation shaft 31 among four sides forming the peripheral portion of the damper plate 30 and have belt-like outer surfaces. When the damper plate 30 is positioned at a position to close a ventilation path 40, the outer surface of the upper peripheral rib 34A becomes parallel with an upper wall surface 13A of the retainer with a narrow clearance therebetween and the outer surface of the lower peripheral rib 34B becomes parallel with a lower wall surface 13B of the retainer with a narrow clearance therebetween.

Abstract: An airflow adjustment member includes the following unitarily formed members: a closing airflow direction adjustment plate, a plurality of rear airflow direction adjustment plates (a first rear airflow direction adjustment plate, a second rear airflow direction adjustment plate, and a third rear airflow direction adjustment plate), and connection members (a first connection member and a second connection member). When air blown out from an air blowing device is to be shut off, an opening portion of the air blowing device is closed by a single closing airflow direction adjustment plate. The positions of front-end portions of the rear airflow direction adjustment plates are determined according to distances of the rear airflow direction adjustment plates from the closing airflow direction adjustment plate.