PURPOSE: To provide a pleated curtain system installed at a window, etc., composed of an abnormally formed frame for exactly closing the window or the like with extension and for easily opening this window or the like with reduction.

CONSTITUTION: A pleated curtain 3 is fitted to a head box 4 at the upper part of a trapezoidal abnormally formed frame 2 while laterally directing its pleats, a bottom bar 6 is attached to the central lower edge of this pleated curtain 3, and the lower edge of a central part 3a of the pleated curtain 3 is moved up by operating an elevating string 7. Thus, the pleated curtain 3 is opened by moving pleated curtains 3b and 3c on both sides upward along side frames 2c and 2d of the abnormally formed frame 2 while bending them.