To open two curtains at a window from the center thereof toward both sides and also close the curtains at the same time to be put together in the central part.

A loop-like cord 5 is wrapped round pulleys 3, 3 respectively journalled to both ends of a guide rail main body, and leading runners 7, 8 slidably fitted in the guide rail main body and the central part of the loop-like cord 5 are connected to each other with a coil spring 36 interposed between them. The coil spring 36 is formed to be shorter than the distance between both stopper pieces 32a, 32b in the state where tension and compressive force are not applied, and both end parts are provided with stop rings 36a, 36b to which the respective ends of the loop-like cord 5 are joined. The respective one ends of the loop-like cord 5 passed through the holes of the stopper pieces 32a, 32b are fastened to the respective stop rings 36a, 36b.