Combined writing tool

A combined writing tool comprising:

• a cylindrical casing:
• a push button extended from a top end of said cylindrical casing by force of a spring;
• a plurality of writing cartridges arranged in said cylindrical casing and adapted to be alternatively extended from a bottom end of said cylindrical casing through a small aperture formed in said cylindrical casing, said writing cartridges comprising a combination of any one of a mechanical pencil a ballpoint pen and a felt-tip pen;
• and
• a cam arranged in said cylindrical casing and adapted to cause a tip of either one of said writing cartridges to be alternatively extended from and retracted in said cylindrical casing through said small aperture in response to a pushing operation of said push button;
• wherein:
• said push button is formed as a cylindrical body having substantially V-shaped recesses formed on a bottom end;
• said cam comprises trapezoidal projections formed on an outer circumferential surface at a lower portion of an upper half portion of said cam, said trapezoidal projections being adapted to be engaged with said substantially V-shaped recesses of said push-button;
• said cam is formed as a cylindrical body in which the upper half portion is adapted to be rotatably and slidably fitted in a central bore formed in said push button, said cam further comprising a pushing rod projected from a bottom end of said cylindrical upper half portion, said pushing rod having a pushing surface at a bottom thereof for engaging a top end of one of said writing cartridges slidably held in a cartridge holder arranged within said casing for pushing the writing cartridge downward:
• said casing is formed, at an upper portion of an inner circumferential surface thereof with a first ridge having a first substantially saw-toothed tip for causing a rotation of said cam through sliding engagement between said first saw-toothed tip and said trapezoidal projection of said cam to push a top end of one of said writing cartridges by said pushing surface and cause a tip of said one of said writing cartridges to be extended through said small aperture, and a second ridge having at least a second substantially saw-toothed tip for causing a further rotatation of said cam through sliding engagement between said at least second saw-tooth tip and said trapezoidal projection of said cause the tip of said one writing cartridge to be retracted into said casing by said force.