Abstract: A supporting bracket including a track member, a slide, a stop member, a sash arm, a short link, a strut and a brace. The track member has a pair of folded side flanges along the length thereof with at least one of the folded side flanges which is subject to face toward a window sash being discontinuous at a central part thereof to define a cutout part; and a boss provided with a pivot pin having a central groove and a C-ring. The slide is movable along the track member and has a length substantially equal to the length of the cutout part. The stop member is secured to the track member and has a button shape with a central groove and a flattened portion. The stop member is turnable to a position with its rounded portion facing the slide to keep the slide within the side flanges and is turnable to a position with its flatten portion facing the slide such that the slide is releasable from the track member at the cutout part.