The present invention provides a screw-type writing instrument having an expansion and contraction function in which an outer shaft cam (10) , a cartridge holder (30) and an inner shaft cam (40) are coupled in a double screw manner, so that the expansion or contraction of the writing instrument and the advancing or retracting operation of a pen core (20) can be simultaneously conducted, thus being convenient to use, and which, thanks to the contractible structure, is convenient to carry and hold. |