To provide a method for stabilizing the shape of a curtain at a low cost, with which labor and difficulty of folding a curtain and mounting of a processing mold, a tool, etc., are removed as much as possible, effective and accurate heat setting is carried out and a tool useful for the method for stabilizing the shape of a curtain.

The tool useful for the method for stabilizing the shape of a curtain is equipped with a plurality of molded members 3 which are each composed of a cylindrically projecting head part 1 and a tabular base part 2 and are overlapped and arranged in an alternately engaged state, guide rods 5 with which the molded members are divided into two parts of the front and the back based on the existence position of a curtain cloth 4 to be laid between the engaging parts of the molded parts and which support the base parts of a plurality of the molded members included at each side slidably in the overlapping direction, an extension urging member 6 for providing uniform extension action to every space between adjacent base parts of the molded member included at each side, a stopper for regulating the slide of the curtain cloth at the engaging part at both the ends of the curtain cloth in the width direction and a locking means 8 for holding the state of engaging part according to the specification of the curtain cloth against extension action.