The invention relates to a writing instrument including a body (2), a clip (5) and a first projecting member (3) for attaching the clip (5) having a first lateral side (33). The clip (5) includes a bar (53) and the body includes a second projecting attachment member (4) having a second lateral side (43). The second lateral side (43) extends from a base (41) secured to the body (2) to an upper end (43a) from which a projection (44) extends towards the first lateral side (33). The first and second lateral sides (33, 43) and the projection (44) are arranged to provide a cavity (49) under the projection suitable for receiving the bar (53), and to provide a passage (48) suitable for inserting a locking element (61) into a locked position for which it is adjusted between the first lateral side (33) and the barrel (53) of the clip located in cavity (49).