To prevent the generation of the state in which lead delivery operations is disturbed by noises of sliding of a knock button with a slider generated when the knock button is pressed or by powder generated by the slide contact of the knock button with the slider or the wear of the slider, and the operation gets slower and finally a lead delivery mechanism is moved forward and not moved backward to the original position.

A writing instrument is disposed in a barrel 1, and the writing instrument is so disposed as to appear and disappear from the barrel, and a window hole is formed on the side wall of the barrel, and a knock piece 3 movable in the diameter direction of the barrel is formed on the window hole, and also a slider 14 movable by the slide contact with the knock pieces is disposed on the writing instrument, and the knock piece and the slider are composed of polyacetal resin and a silicone lubricant is contained at least in one member.