Patent ID: 7527445

Claim:
A writing instrument comprising: a tubular casing having a through-hole extending in a longitudinal direction of the casing, a wall surface, and two apertures formed in the wall surface; a writing refill inserted in the through-hole of the tubular casing for extension out of the casing to a writing position and retraction into the casing to a retracted position; a rotary cam mechanism accommodated in the through-hole of the casing for extending and retracting the writing refill between the writing position and the retracted position, respectively, the rotary cam mechanism comprising a cam cylinder inserted into the through-hole of the casing from a rear end thereof and having a stationary cam and two projections that have vertical edge surfaces on rear ends thereof engageable with respective ones of the two apertures of the casing to prevent movement of the cam cylinder relative to the casing in the longitudinal direction and disengageable from the apertures in response to rotational movement of the cam cylinder relative to the casing in a direction of rotation to permit withdrawal of the cam cylinder from the rear end of the casing, a rotary cam engageable with the stationary cam of the cam cylinder, and a knocking cam engageable with the stationary cam of the cam cylinder and the rotary cam; and a knocking member integrally connected to the knocking cam and connected to the cam cylinder in a non-rotatable state while permitting movement of the knocking member relative to the cam cylinder in the longitudinal direction.