An air-conditioning case of an air-conditioning unit forms air passages therein. A film member is reciprocably supported in the case and has free ends. Reinforcing members are secured to the lower end of the film member. A drive force for reciprocating the film member is applied to the film member from a motor through a drive shaft and drive gears, which are attached to the drive shaft, to open and close the air passages with the film member. When the film member is moved upwardly, the reinforcing members abut against positioning portions of the case to position the film member at a predetermined position.