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 hook portion 23 for catching a finger or the like is provided at a position circumferentially shifted 90° from a protruding piece 19 on a side surface 8a close to an insertion port 7 of a body portion 8 of the pen tip protecting adaptor 6 so as to extend through the side surface.