Air passage opening/closing device

The air passage opening/closing device comprising:

• a case which forms an air passage,
• a slide door which has a door body part made of plastic formed in a plate-shape, which is arranged to be able to slide in the case, and which opens and closes the air passage;
• and
• a gear mechanism which drives the slide door,
• wherein the case is formed with guide grooves which are positioned at two sides of the air passage in a width direction of the door body part and each of which is comprised of a case side seal surface which the door body part abuts against and a guide wall surface which faces the case side seal surface,
• two end parts of the door body part in the width direction are arranged inside of the guide grooves,
• the gear mechanism has at least one driven side gear which is provided at the door body part and at least one drive-side gear which engages with the driven side gear,
• the driven side gear is formed to extend in parallel with a movement direction of the slide door at a portion positioned at the inside in the width direction from the guide grooves at the door body part,
• a portion of the door body part facing the guide wall surface or a portion of the guide wall surface facing the door body part is formed with interposed parts which are interposed between the door body part and the guide wall surface, and
• said interposed parts have a bending rigidity in the movement direction of said slide door higher than the teeth of said driven side gear.