Abstract: The device comprises a foldably extensible and collapsible shade member, and means for forming corresponding sets of laterally projecting trunnions at spaced intervals along opposing edges of the shade member. It also comprises a pair of elongated track defining members which are adapted to be mounted on opposing sides of the window frame so that tracks thereof are oppositely disposed to one another across the frame. The track defining members have opposing sets of carrier elements slidably engaged on the respective tracks thereof, which are adapted to support the trunnions of the shade member on spaced parallel axes extending crosswise the sides of the frame. In addition, there are means for extending and retracting the shade member when the trunnions thereof are supported on the sets of carrier elements, and means whereby the respective sets of carrier elements and trunnions can reciprocate in relation to one another along the aforesaid axes when the shade member is extended and retracted thereon.