PURPOSE: To enable handy application of the title pen at the time of use of a no-carbon paper by a terminal user and make it possible to decolor a developed color part or to prevent color development at a part at which color development is unrequired, by filling a felt-tip pen type container with a composition in which the weight ratio of a desensitizer solution to a volatile solvent is set in a specified range.

CONSTITUTION: A desensitizer dispersed in a volatile solvent is contained in an ink-containing space part 1 in a writing barrel part 3. When this pen is used, the desensitizer permeates into a felt-made writing tip 2 supported by a holder 4 and a tip support part 5, and the desensitizer is moved from the space part 1 to the front end part of the writing tip 2 making contact with a paper. A composition comprising the desensitizer solution and the volatile solvent in a weight ratio of 95:5W20:80 is contained in the apace part 1 of a felt-tip pen type container. This felt-tip pen is useful in decoloring a developed color part or preventing color development at a part at which color development is unrequired, without leaving any apparently conspicuous marks, in use of a no-carbon paper.