Abstract: Disclosed herein is a folding security window, in which an end of the security window is mounted to a window sill, the other end of the security window is connected to a window, a height-adjustable movable part is mounted to a vertical pole of the security window, a connecting means for connecting or disconnecting the security window to or from the window is provided, and the folded security window is not exposed to the outside. When the window is opened or closed, the security window is unfolded or folded, so that the security window does not spoil the appearance of the city. The movable parts mounted to upper and lower ends of the vertical pole enhance the adaptability and movability of the security window. The security window efficiently performs its original function without hindering ventilation, views, or light admittance.