Patent ID: 6883996

Claim:
A writing instrument comprising: a pen shaft having a leading holder at a leading end thereof; a pen core placed in the leading holder, the pen core being movable in the leading holder along the longitudinal direction of the pen shaft; an ink storage chamber formed in the pen shaft for storing ink; a valve operable to be in contact with the pen core for allowing the ink to flow to the pen core when the pen core is applied with a pressure in a tail direction, and keeping the ink from flowing to the pen core when the pen core is applied with no pressure; wherein: the pen core is formed with a projection on a base end thereof, the projection extending in a direction normal to the longitudinal direction of the pen shaft; and the leading holder is formed with an engaging portion operable to come into contact with the projection of the pen core, the engaging portion extending inward from an inner circumferential surface of the leading holder, the engaging portion being operable to engage with the projection of the pen core to thereby prevent the pen core from coming out of the leading holder; and the projection is shaped to gradually reduce its projecting amount as advancing in the tail direction.