PURPOSE: To prevent the tilting of a moving frame, and to form the change- direction member of a cord in simple structure.

CONSTITUTION: One cord 8 vertically holding a moving frame 5 to guide frames 4 and moving direction the moving frame 5 is used. Fixing points 7A, 7B at both ends of the cord 8 are set to the moving frame 5. The cord 8 is wound among the two guide frames 4, a housing frame 2, an opposed frame 3, the moving frame 5 and a folding body 1. At least either one of the fixing points 7A, 7B at both ends of the cod 8 is used as the tension adjusting section of a cord, a place thereof is A section freely the longitudinal direction of the moving frame 5. A section on its midway of the cord 8 is fixed by the section of the moving frame 5.