Abstract: Air-cooling and tempering a glass sheet is performed while the glass sheet is continuously conveyed without adversely affecting the quality of the glass sheet. It is provided with a conveying means (22) installed to be operable from a forming zone to a cooling area, a plurality of upper blowing members (24A to 24J), a plurality of lower blowing members (26A to 26J), a plurality of air-supply boxes (100, 102) for controlling blow/stop operations of cooling air from each of the blowing members and an air-supply source (200) connected to these air-supply boxes. Each of the air-supply boxes has a cylindrical damper (130), casings (134, 136) and a slide bearing (144) provided in a space between the damper and the casing, wherein the cool-air supplied from the air-supply source can be supplied to the upper and lower blowing members through the air channels by adjusting the rotational positions of the dampers.