To provide a writing implement to which a phase change or an indicator function in consequence of a temperature change can be given when a decoration part such as a decoration body, an inner tube or the like that is visually recognized through an outer tube changes reversibly to visually recognizable and visually unrecognizable states according to the temperature change in the writing implement using a double-tubular barrel, and which is equipped with an interesting and unexpected decorative effect.

The writing implement 1 uses the double-tubular barrel 2 of the inner tube 5 in which a writing implement unit 9 is prepared, and the outer tube 6 which covers the inner tube 5. The outer tube 6 has a reversible thermal discoloring capability and has reversible visual functions of being a transparent state in which the interior is visually recognizable from outside by the temperature change, and being a visually unrecognizable concealment state.