a combined writing tool comprises a cylindrical casing ; a push button extended from the top end of said cylindrical casing by force of a spring ; a plurality of writing cartridges arranged in the casing and adapted to be alternatively extended from the bottom end of the casing through a small aperture formed therein ; and a cam arranged in the casing and adapted to cause a tip of either one of the writing cartridges to be alternatively extended from and retracted in the casing through the small aperture in response to the pushing operation of the push button . the combined writing tool makes it possible to extend or retract either one of the writing cartridges from or into the casing through the small aperture only by a pushing operation of the push button . thus easy operation can be obtained and unwanted extension of the writing cartridge can be prevented . in addition , it is possible to prevent an erroneous operation during an exchange of the writing cartridge , to enable an easy one - hand operation , to improve the reliability of the mechanism , and to reduce a size of the mechanism .