Patent ID: 7644526

Claim:
An extension tool for a sheet-shaped material, said extension tool comprising: four corner members being placed at the four corners of a rectangle; four frame members, both ends of each of said frame members being supported by said corner members, each of said frame members being placed between two opposite corner members, being able to move in a direction toward the two opposite corner members, and being able to move in a direction approaching or in a direction away from the opposed frame member together with the two opposite corner members supporting both ends of the frame member in relation to the opposed frame member; four solid rods, each passing through one of said frame members and placed between two opposite corner members, and each solid rod having collars at positions closer to the ends thereof; and elastic members, each being disposed between each of said collars and an outer edge of an adjacent one of said corner members so that the elastic members push one end of said solid rod in a direction toward the adjacent corner member and the other end of said solid rod in a direction toward the opposite one of said corner members, wherein each of said frame members has an anchoring element where a peripheral portion of the sheet-shaped material or a frame for stretching the sheet-shaped material is anchored; and wherein each of said four frame members is able to move in a direction toward and away from said opposite corner members and in an approaching direction or in a direction away from the opposed frame member.