Abstract: A device for advancing and retracting a writing element in a writing instrument, of the type comprising a cylinder, a stationary cam provided on an inner surface of the cylinder, a rotary cam follower disposed inside the stationary cam to be rotatable and slidable axially of the cylinder, the rotary cam follower being in abutting engagement at a front end thereof with the writing element, and a knocking rod disposed in the cylinder and having a front cam portion. When the knocking rod is pushed forward, the knocking rod, the stationary cam and the rotary cam follower cooperate to advance the writing element and maintain the same in an advanced position and to allow the writing element to retract to a retracted position. The knocking rod has projections which are in slidable engagement with slots formed axially through the cylinder. The knocking rod has slots to make it resilient.