Abstract: An extendable elastic cord is fastened with one writing instrument which connects with a base of the pen holder for users of pen to write or take notes by drawing the pen out of the holder and the pen never separates from the base of the pen holder, wherein the said pen holder is comprised of a base which includes a left cover and a right cover, an automatic coil apparatus and a detent device. The automatic coil apparatus of the present invention consists of a bearing tube, a tube lid, a spiral spring, a winding wheel and a binding cord. The detent device of the invention includes a rubbing plate, a leaf spring, a detent rod and a spring. The automatic coil apparatus and the detent device are installed inside the body of left cover.and right cover to integrate as a whole.