PROBLEM TO BE SOLVED: To provide an opening/closing device for a ventilation window, in which operation is easy, a ventilation window is smoothly opened and closed, an opening/closing position is reliably and rapidly set, an opening position of the window is firmly held by brake work, without rattle due to strong wind or the like, and robustness is exhibited.SOLUTION: A ventilation window installed at a gable side of a greenhouse opens/closes by that, according to movement of a rotation shaft via driving means positioned at one side end of a window frame when operating a rope, a base part is pivoted to an L-shaped member fastened to the rotation shaft and a curved arm whose tip is pivoted to a vertical member of the wind frame pushes/pulls the window； the driving means comprises a power transmission part and a speed-reducing mechanism in a casing； and when the rope is operated and the curved arm is stopped at a predetermined position, a break in the power transmission part works and an opening state of the positioned ventilation window is held.【課題】操作が簡単で換気窓の開閉がスムーズになされ、開閉位置も確実迅速に設定でき、ブレーキが働いて窓の開口位置を確固として維持し強風等にもガタを生ずることなく堅牢性を発揮する換気窓開閉装置を提供する。【解決手段】温室の妻側に設置した換気窓が、ロープを操作すると窓枠の一側端に位置する駆動手段を介して回転軸が可動するのに伴い、回転軸に固着したＬ字部材に基部を枢着し且つ先端部を窓枠の縦材に枢着した湾曲アームの押し引きによって開閉し、前記駆動手段はケーシング内に伝動部と減速機構を備え、ロープを操作して湾曲アームを所定位置で停止すると伝動部内のブレーキが働いて位置決めされた換気窓の開口状態が保持される。【選択図】図２
