An apparatus for window is used for moving a movable window plate among an insertion position for being inserted into an aperture portion of a fixed window plate, an extraction position for being extracted from the aperture portion toward an indoor side, and an opening position for being moved from the extraction position in a sliding direction that is different from an inserting and extracting direction to open the aperture portion. The apparatus includes a rotating shaft rotatably supported at a predetermined position for the movable window plate; a movement conversion mechanism configured to convert a rotation of the rotating shaft into a translation of the movable window plate between the insertion position and the extraction position; and a drive shaft, fixed to the rotating shaft, configured to rotate the rotating shaft around a central axis of the rotating shaft by revolving around the central axis of the rotating shaft.