Abstract: Provided is an ink introducing tube which realizes a stabilized ink supply from an ink tank located at the rear portion of a felt pen into a tip at the front end thereof, and a writing instrument incorporating it. On the inner peripheral wall of an ink introducing tube through which an ink tank is communicated with a tip located at the front end, a plurality of protrusions are formed to provide therebetween a passage for downward flow which utilizes the capillary action of the protrusions, and the interior space of the ink introducing tube which is surrounded by the tips of the plural protrusions is formed as a large space so that the capillary action can take place. Thus, the flow of air to the ink tank moves upwardly through the interior space while changing into air foam during the ascent, whereas the ink flows downward while being retained between the protrusions. Therefore, replacement of the ink by the air can be performed smoothly whereby ink blobbing is prevented and flawless writing is realized.