To facilitate detachment of a pen tip protecting adaptor from a container body in an ink storage container including the container body containing writing material ink and the pen tip protecting adaptor inserted thereto, the adaptor having an ink accumulation portion for accumulating the writing material ink.

A protruding portion 19 with a male thread portion 18 formed at the tip which can be inserted into a body portion 8 of the pen tip protecting adaptor 6 is provided on the outer surface of a head end portion 3a of a cap 3. A female thread portion 21 capable of being screwed to the male thread portion 18 of the protruding portion 19 is formed on an inner wall surface 8a in the vicinity of an insert port 7 of the body portion 8 of the adaptor 6. The cap 3 is connected to the adaptor 6 by screwing the female thread portion 21 to the male thread portion 18 of the protruding portion 19, so that the adaptor 6 can be pulled out of the container body 2 by the cap 3.