A structure of a damper for a duct is provided to open and shut a path through blade members of which ends move in opposite directions to control an amount of air passing through a duct accurately in accordance with an angle controlled by rotation of rotary shaft members, and control an air amount precisely to increase the ventilation efficiency and convenience. A plurality of rotary shaft members(10) pass through a side of a duct(1) for being combined with the duct rotatably, and are formed at certain gaps. A blade(20) is mounted at each rotary shaft member for opening and shutting a path(1a) of the duct. An operation handle member(30) is combined with any one rotary shaft member at the outside of the duct, having a handle part(31). A handle locking unit(40) locks and unlocks a position of the operation handle member. An inverse rotation link member(50) connects the rotary shaft members with one another, and rotates the rotary shaft members in opposite directions alternately.
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